Fasteners and Threads Lesson Test

Answer: C

Correct answer: A bolt. A bolt is an externally threaded fastener that passes through unthreaded clearance holes in both parts, and a nut tightened on its end stretches the bolt slightly. That stretch creates clamping force that squeezes the plates together. The distinction from a screw is that a screw usually threads into one of the parts. Pins and rivets serve other purposes: a cotter pin keeps a nut from backing off, and a dowel pin locates parts.

• A: A cotter pin is commonly a retention device rather than the primary clamp.
• B: A dowel typically locates parts, not a conventional bolted clamp.
• C (correct): A bolt can pass through clearance holes and engage a matching nut to clamp the plates.
• D: A blind rivet makes a different type of joint without a separate threaded nut.

Answer: A

Correct answer: A tap. To make internal threads, a hole is first drilled to the tap-drill size given in a chart, slightly smaller than the screw's major diameter, leaving material for the threads. The tap is then turned in with a tap wrench, often with cutting oil and periodic reversing to break chips. A helpful memory aid: taps work inside holes, dies work outside rods. A countersink only shapes the hole's entrance for a flat head.

• A (correct): A tap forms or cuts mating threads inside a suitable predrilled hole.
• B: A die is generally used for external threads on a rod or similar workpiece.
• C: A countersink makes a tapered recess for a matching head.
• D: A punch marks or displaces material, rather than creating machine-thread geometry.

Answer: C

Correct answer: A die. A threading die is a hardened ring with cutting edges inside; it is held in a diestock and turned onto the end of a rod to form external threads, similar to a nut that cuts. The rod is usually chamfered at the end so the die starts straight. A tap is the matching tool for internal threads, so the two are easy to mix up. Remember that a tap goes in and a die goes around.

• A: A feeler gauge checks small gaps instead of cutting threads.
• B: A socket wrench transmits torque to a drive feature but does not make threads.
• C (correct): A die is an external-threading tool and must match the required thread size and system.
• D: A tap cuts or forms internal, not external, threads.

Answer: C

Correct answer: Thread pitch in millimeters. In an ISO metric callout, the M means metric thread, the first number is the nominal major diameter in millimeters, and the number after the × is the pitch, the distance between adjacent threads. So M8 × 1.25 is an 8-mm thread with crests 1.25 mm apart. When the pitch is omitted, coarse pitch is assumed, and 1.25 mm is the standard coarse pitch for M8. Torque and head size come from other references.

• A: The 1.25 number does not denote threaded length in inches.
• B: A thread callout is not a universal tightening-torque instruction.
• C (correct): For a metric thread, the value following the multiplication sign commonly denotes axial pitch in millimeters.
• D: Nominal hex-head width is a separate head dimension, not the pitch number.

Answer: D

Correct answer: Twenty threads per inch. Unified inch threads are written as diameter followed by threads per inch, so 1/4-20 means a quarter-inch nominal diameter with 20 threads in every inch of length. This is the coarse (UNC) series for that size; the fine series is 1/4-28. Metric threads work the other way, listing the pitch distance in millimeters. A thread pitch gauge or a ruler can confirm the count by checking threads along one inch.

• A: Millimeter pitch notation uses a different thread designation system.
• B: A 20-TPI designation does not set the number of turns needed to seat a joint.
• C: Thread count is a geometric measure, not a torque specification.
• D (correct): The designation gives nominal quarter-inch diameter and 20 threads per inch.

Answer: D

Correct answer: A flat washer. A flat washer is a thin disk placed under a nut or bolt head. Its larger outside diameter spreads clamping force over more area, reducing the chance of crushing soft material such as wood or aluminum, and it gives the turning nut a smooth surface instead of scraping the part. It can also bridge an oversized or slotted hole. Taps and dies are tools for making threads, not parts left in the assembly.

• A: A tap manufactures internal thread geometry rather than furnishing a bearing face.
• B: A die forms external threads and is not part of the installed washer stack.
• C: A cotter pin secures certain nuts against rotation, not broad bearing contact.
• D (correct): A flat washer can spread bearing contact or protect the surface when specified.

Answer: A

Correct answer: Countersunk flat head in a matching recess. A flat-head screw has a cone-shaped underside, commonly 82 degrees for inch screws and 90 degrees for metric screws. A countersink bit cuts a matching cone in the hole, so the head drops in until its top is level with the surface. The countersink angle must match the head, or it will sit high or bear on a small ring. Pan and hex heads have flat undersides, so they rest on top.

• A (correct): The conical underside of a matching countersunk flat head can seat approximately flush with a prepared countersink.
• B: A socket cap head normally needs a different recess geometry to be flush.
• C: A pan head generally remains above the surface without special counterbore design.
• D: A hex head projects above the panel, violating the flush requirement.

Answer: C

Correct answer: Clockwise tightening viewed from the drive end. Most threads are right-handed, which gives the familiar rule righty-tighty, lefty-loosey: turning clockwise as you face the head or nut advances it. Left-hand threads reverse this and are used where normal rotation could loosen a part, such as the left pedal of a bicycle or some grinder arbors. They are often marked with notches or an LH label, so check before applying force.

• A: Counterclockwise is the opposite direction for a typical right-hand tightening motion.
• B: Clockwise is normally tightening, not loosening, for common right-hand threads.
• C (correct): Most ordinary right-hand threads tighten with clockwise motion as viewed from the drive end, when mating conditions are conventional.
• D: Left-hand threads are an intentional exception to the common convention.

Answer: B

Correct answer: To locate or align mating parts. A dowel pin is a precisely ground cylinder pressed or slip-fitted into matching holes in two parts. Because the holes and pin are made to tight tolerances, the parts return to exactly the same position each time they are assembled. Bolts supply the clamping force, while dowels prevent sideways shifting and set location. A dowel has no threads, so it cannot tighten anything or cut threads.

• A: A dowel does not provide controlled threaded tightening moment.
• B (correct): A dowel pin frequently positions components with repeatable alignment in appropriately sized holes.
• C: Alignment does not guarantee the dowel carries all required clamping loads.
• D: Thread cutting requires an appropriate tap or forming tool.

Answer: D

Correct answer: Stop and verify thread condition and compatibility. A correctly matched nut should spin on by hand for several turns, so binding at the start signals a problem such as cross-threading, a wrong pitch, damaged threads or dirt. Back the nut off, check the threads with a pitch gauge or a known good nut, clean them and restart it square. Forcing it with leverage or an impact tool tends to strip the threads and turns a quick check into a repair.

• A: Using a longer handle on a binding nut adds uncontrolled load and risks stripping the thread or causing cross-thread damage.
• B: Impacting a binding nut forces mismatched or damaged threads together and can ruin both parts.
• C: A threaded joint should not rely on forced wear-in of a mismatched profile.
• D (correct): Unexpected early binding calls for inspection of alignment, contamination, pitch, handedness, and thread damage.

Answer: A

Correct answer: M10 × 1.5 bolt with M10 × 1.5 nut. A threaded pair mates only when the nominal diameter and the pitch both match within the same thread system. In a callout such as M10 × 1.5, the M means metric, 10 is the nominal diameter in millimeters, and 1.5 is the pitch in millimeters. A tempting mistake is to trust a near match: an M10 × 1.25 nut may start on the bolt but will cross-thread, and an inch nut such as 3/8-16 looks similar in size but uses a different system entirely.

• A (correct): Both nominal metric diameter and metric pitch match in the correct pair.
• B: These parts share diameter but differ in metric pitch.
• C: An inch-based thread specification is not interchangeable from apparent size alone.
• D: An 8 mm nut has a different nominal diameter from an M10 bolt.

Answer: A

Correct answer: It has more threads per inch and a finer pitch. In Unified callouts the first number is the nominal diameter and the number after the dash is threads per inch (TPI). Pitch is 1 divided by TPI, so 1/4-20 has a pitch of 0.050 inch while 1/4-28 has about 0.036 inch, a finer thread. The common trap is assuming a bigger number means a bigger or coarser thread; it actually means the threads are packed closer together on the same quarter-inch diameter.

• A (correct): The suffix 28 is larger TPI, so axial spacing per crest is smaller than for 20 TPI.
• B: The suffix describes how many threads fit in one inch, not the required torque in newton-meters for that assembly.
• C: Both labels have the same nominal quarter-inch diameter; the significant difference is the 20 versus 28 threads-per-inch specification.
• D: A higher threads-per-inch number indicates smaller axial crest spacing, which defines a finer rather than a coarser thread.

Answer: D

Correct answer: 0.050 inch. Pitch is the distance from one thread crest to the next, and for an inch thread it equals 1 divided by TPI. Lead is how far the screw advances in one full turn; on a single-start thread, lead equals pitch. So

A frequent error is dividing or shifting the decimal incorrectly, which gives 0.020 or 0.200 inch. Check by reversing: 20 turns × 0.050 inch = 1 inch.

• A: 0.020 inch per turn would correspond to 50 threads per inch, not 20.
• B: Twenty inches is a length far larger than the stated crest spacing.
• C: 0.200 inch corresponds to only five pitches per inch, not 20.
• D (correct): Lead equals pitch for a single-start thread: one inch divided by 20 equals 0.050 inch.

Answer: D

Correct answer: 5.0 mm. On a single-start thread, each full turn advances the screw by exactly one pitch, so total travel is pitch multiplied by the number of turns: 1.25 mm × 4 = 5.0 mm. Think of the thread as a ramp that moves the screw a fixed amount per revolution. The tempting mistake is dividing instead of multiplying, which gives a tiny value; more turns must always mean more travel, never less.

• A: 1.25 mm is the travel for one, not four, turns.
• B: Dividing pitch by the number of turns gives smaller rather than accumulated travel and reverses the correct multiplication.
• C: 20 mm would require a five-millimeter lead, not 1.25 mm.
• D (correct): Axial travel equals pitch times turns: 1.25 × 4 = 5.0 mm.

Answer: C

Correct answer: 3.0 mm per turn. Pitch is the crest-to-crest spacing measured along the axis, while lead is the distance the screw advances in one full turn. A multi-start thread has several interwoven helixes, so each turn advances by the pitch times the number of starts: 1.5 mm × 2 = 3.0 mm. The usual mistake is treating pitch and lead as the same, which is only true for single-start threads. Multi-start threads are used where fast travel is needed, such as on bottle caps.

• A: 1.5 mm would describe a single-start thread of that pitch.
• B: Dividing 1.5 mm by two incorrectly treats the number of starts as a divisor instead of a multiplier.
• C (correct): Lead is pitch multiplied by the number of starts: 1.5 × 2 = 3.0 mm per revolution.
• D: 6.0 mm would correspond to four starts with 1.5 mm pitch.

Answer: B

Correct answer: It can be installed with access from only one side. A solid rivet is set by deforming its tail with a bucking bar or tool on the far side, so both faces must be reachable. A blind rivet, often called a pop rivet, is inserted and set from one side: pulling its mandrel expands the body behind the material. That is why it is used on closed tubes, panels and boxes. It is not inherently stronger than a solid rivet, and it needs no separate nut.

• A: Blind rivets are set by pulling a mandrel or stem, not by a machine thread, so threading is not their defining feature.
• B (correct): A blind rivet is set entirely from the near side, so it suits joints where the back face cannot be reached.
• C: Strength depends on rivet design and application; a universal superiority claim is false.
• D: Needing a nut on the far side would require back access, which is exactly what a blind rivet avoids.

Answer: D

Correct answer: To resist unintended rotational loosening. A prevailing-torque nut, such as a nylon-insert or deformed-thread locknut, adds friction that must be overcome to turn it at any point, not just when it is tight. That extra drag helps keep the nut from backing off under vibration. The resistance is not a measure of clamp load, and because the locking element wears or deforms with each use, manufacturers often limit reuse. Treat a nut that spins on freely as worn out.

• A: A prevailing-torque nut mates with existing threads rather than cutting a stud.
• B: Prevailing-torque features wear with each use, so reuse is often limited by the manufacturer and the application.
• C: The extra turning resistance is not a gauge of clamp load and does not directly measure preload.
• D (correct): The nut includes a feature that resists free rotation beyond normal thread contact.

Answer: B

Correct answer: Mechanical retention against full nut rotation. A castle nut has slots cut across its top, and the stud has a drilled cross hole. When a slot lines up with the hole, a cotter pin passes through both and is bent over, so the nut cannot turn off even if it loosens slightly. This positive locking is common on axle and steering components. The pin does not set or indicate preload; correct torque is applied first, then the nut is aligned to the next slot.

• A: It retains a nut rather than changing thread geometry.
• B (correct): The pin physically blocks rotation of a suitably slotted nut in a designed assembly.
• C: The pin prevents a defined rotation path but cannot indicate the axial tension or clamping force in the bolt.
• D: A cotter pin is a thin split pin with no broad bearing surface, so it cannot spread load the way a washer does.

Answer: A

Correct answer: A bolt turns without building the expected clamp. Tightening a bolt normally stretches it slightly and squeezes the joint, so wrench resistance rises steadily as the parts clamp. If the internal threads are stripped, the bolt spins or keeps turning without that rising resistance because the thread flanks are no longer holding. Washers, grade markings and nearby tools say nothing about thread condition. When this happens, stop tightening and inspect, since forcing it usually damages the hole further.

• A (correct): Stripped mating threads can allow rotation without the intended tensile and clamping response.
• B: Washer presence does not prove thread integrity or failure.
• C: A tool being available says nothing about the state of the threaded material.
• D: A correct grade marking describes the bolt's strength, not whether the mating internal threads are still intact.

Answer: C

Correct answer: It can distribute bearing load but does not guarantee anti-loosening. A flat washer spreads the clamping force of a bolt head or nut over a larger area, which protects soft or finished surfaces and can bridge an oversized hole. It has no feature that resists rotation, so it should not be counted on to prevent loosening under vibration. Locking requires a different method, such as correct preload, a prevailing-torque nut, a cotter pin or a threadlocker. A washer also cannot make up for too little thread engagement.

• A: Washer placement does not change the right- or left-hand helix.
• B: A plain flat washer has no locking feature, so it cannot be relied on to keep a nut from loosening under vibration.
• C (correct): A flat washer mainly serves a bearing or surface-protection role when properly specified.
• D: A washer only sits under the head or nut; it cannot replace the load-carrying engagement of the threads.

Answer: C

Correct answer: Applied torque may rise without generating intended joint clamp. Torque is only a stand-in for clamp force: tightening is supposed to stretch the fastener and press the joint parts together. If a stud bottoms in a blind hole, the wrench meets resistance from the stud jamming against the hole bottom instead of from the joint clamping. The torque wrench may click while the parts are still loose. Checking stud length against hole depth before assembly avoids this false reading.

• A: Bottoming stops the stud's travel; it does not change the stud's nominal or outside thread diameter.
• B: A blind hole does not universally require a washer at its bottom.
• C (correct): Contact at the bottom can prevent the mating parts from clamping despite wrench resistance.
• D: Drive recess shape is not established by bottoming behavior.

Answer: A

Correct answer: Its grade, surface conditions and service environment must match the application. Threadlocker is an anaerobic adhesive that cures in the absence of air between metal threads, filling gaps so the parts resist turning. Its performance depends on the strength grade chosen, clean and suitable surfaces, and the temperature and chemicals it will see. It is a supplement to proper torque and the correct bolt grade, not a substitute, and it cannot rebuild stripped threads. Removable and permanent grades exist for different service needs.

• A (correct): A threadlocker may help retention only under suitable product and installation conditions.
• B: Threadlocker cure and holding performance vary with the product, temperature and service conditions.
• C: Locking the thread does not change an inadequate fastener material grade.
• D: An adhesive can resist rotation when specified, but it cannot rebuild damaged metal thread flanks that carry the mechanical load.

Answer: A

Correct answer: Initial clamping force produced by elastic deformation. When a bolt is tightened, it stretches slightly like a stiff spring while the clamped parts are compressed. That elastic stretch creates a tension in the bolt and an equal clamping force on the joint, called preload. Adequate preload keeps the joint from separating or slipping under service loads and helps resist loosening and fatigue. It is created during assembly, not after failure, and is unrelated to wrench size or thread count.

• A (correct): Preload is the initial tensile stretch and associated joint compression established during assembly.
• B: Preload is established during proper tightening, before the joint is put into service, not after a failure.
• C: Wrench head size is not a measure of the resulting internal clamp.
• D: Thread count or pitch describes geometric spacing and provides no measurement of tensile preload installed into the bolted joint.

Answer: C

Correct answer: It changes friction at the thread or bearing interfaces. Most of the torque applied to a bolt is used up overcoming friction under the head or nut and in the threads; only a small share actually stretches the bolt. Lubricant lowers that friction, so the same torque produces more preload, which can overstretch a bolt if dry torque values are used. The geometry, starts and diameter of the bolt do not change. This is why specifications state whether a torque value is for dry or lubricated threads.

• A: Lubricant does not convert a multi-start thread into a single-start profile.
• B: Lubrication does not multiply the metal thread diameter by two.
• C (correct): Thread and bearing friction consume part of turning effort, so changes can alter achieved preload.
• D: Torque and length have different units and are not automatically equal.

Answer: B

Correct answer: Tension acts along its axis; shear acts transverse to it. Direction relative to the bolt axis decides the load type. Tension pulls along the axis, trying to stretch the bolt or strip its threads, as with a cylinder head bolt. Shear acts across the axis, trying to slice the bolt where the joined plates slide past each other, as with a trailer hitch pin. Picture scissors: the blades move sideways past each other, which is shear. Both loads occur in metal and wood joints.

• A: Mechanical shear is a force/deformation concept, not simply heat transfer.
• B (correct): Axial pulling is tension, whereas transverse sliding tendency creates shear loading.
• C: Shear is normally transverse, not necessarily parallel, to the axis.
• D: Metal, wood, and many other joints can be under tensile load.

Answer: B

Correct answer: Fatigue with local stress concentration. Fatigue is cracking caused by repeated loading, even when each load is well below the strength that would break the part in one pull. Sharp changes in shape, such as the thread root or the fillet under the bolt head, concentrate stress, so fatigue cracks usually start there. A crack grows a little with each cycle until the remaining metal fails suddenly. A cracked fastener should be replaced, never treated as cosmetic.

• A: A crack at the thread root is damage, not a process that reduces the thread pitch or improves its geometry.
• B (correct): Repeated stresses and thread-root geometry can contribute to fatigue crack development.
• C: Cracks in a loaded fastener require appropriate evaluation, not blanket dismissal.
• D: A crack weakens a loaded part and does not increase the material strength or proof-load capacity of the fastener.

Answer: D

Correct answer: Jaws sprung enough to cause slippage. OSHA's construction hand-tool rule prohibits using wrenches, including adjustable, pipe, end and socket wrenches, when the jaws are sprung to the point that slippage occurs. Sprung jaws no longer grip the fastener's flats, so the wrench can slip suddenly, rounding the fastener and throwing the user's hand or body into nearby objects. A sound, correctly sized socket and a clean bolt head are signs of good practice. Damaged wrenches should be removed from service.

• A: A clean head may support good engagement rather than create the stated hazard.
• B: Normal storage on a rack is unrelated to jaw deformation.
• C: A properly fitting undamaged socket is not by itself the prohibited condition.
• D (correct): OSHA 1926.301 addresses wrench jaws that have sprung enough to permit slipping.

Answer: C

Correct answer: Provide a controlled smooth bearing or pivot surface. A shoulder screw, also called a shoulder bolt, has a precision-ground unthreaded shank between the head and a shorter threaded end. When tightened, the threads clamp only up to the shoulder, leaving the smooth shank as a pin that parts can rotate or slide on, such as a pulley, lever or linkage arm. Its length is chosen so moving parts keep some running clearance. It is not a self-tapping or universal retaining device.

• A: Retention details are application specific; a shoulder screw alone is not universal.
• B: A linkage may need intentional running clearance for movement.
• C (correct): A precision unthreaded shoulder can serve as a guiding or pivot feature in an engineered assembly.
• D: The shoulder is not designed primarily to create arbitrary new thread holes.

Answer: C

Correct answer: Nothing certain about thread diameter or pitch from wrench size alone. Wrench size refers to the distance across the flats of the hex, and different standards and nut styles use different hex sizes for the same thread. A metric and an inch nut, or two nuts with different pitches, can easily share one wrench size. Thread size, pitch, handedness and grade must be identified separately with a thread gauge, caliper, markings or the parts documentation. Matching tool fit only tells you the outside hex shape matches.

• A: Left-hand or right-hand thread direction cannot be proved by the outside hex size of a nut.
• B: Grade cannot be established from a common wrench opening alone.
• C (correct): Head or across-flats dimensions do not uniquely specify complete thread identity.
• D: Two nuts can share a wrench size yet have different thread pitches, so matching hex size proves nothing about pitch.

Answer: D

Correct answer: 6 turns. Each full turn of a single-start thread advances the screw by one pitch, so the number of turns needed is distance divided by lead:

Check it by multiplying back, since 6 turns × 1.5 mm = 9 mm. A common error is multiplying distance by pitch, which gives 13.5 and mixes up the units. Another is confusing the travel in millimeters with the number of turns.

• A: Nine turns at a lead of 1.5 mm per revolution would advance 13.5 mm, exceeding the specified travel.
• B: Multiplying distance by pitch gives a number with incorrect unit logic.
• C: Three turns multiplied by the 1.5 mm-per-turn lead would advance only 4.5 mm, not the stated 9 mm.
• D (correct): Turns equal distance divided by lead: 9 mm ÷ 1.5 mm per turn = 6.

Answer: B

Correct answer: 0.0625 inch. Threads per inch counts how many crests fit in one inch, and pitch is the spacing between neighboring crests. They are reciprocals: pitch = 1 ÷ TPI, so

or one sixteenth of an inch. The common trap is treating the TPI number as a distance. A quick sanity check is that pitch must be a small fraction of an inch, and

• A: 16 inches confuses number of threads per inch with pitch distance.
• B (correct): Pitch in inches is the reciprocal of TPI: 1/16 = 0.0625 inch.
• C: 0.016 resembles a misplaced decimal and would imply 62.5 TPI.
• D: The value 0.16 inch is not the reciprocal of 16 threads per inch and overstates the correct pitch.

Answer: D

Correct answer: 7 N·m. Torque measures how strongly a force tends to rotate an object about a pivot. It equals the force times the perpendicular distance from the pivot to the line of the force, so units are newtons times meters, N·m. Here

N·m. Dividing by the arm length or adding the two numbers gives wrong values. This is why a longer wrench handle makes a stuck bolt easier to turn.

• A: 175 arises from dividing force by 0.20 rather than multiplying.
• B: 0.175 is too small for the given perpendicular lever arm.
• C: Adding force and length gives neither a correct torque unit nor a result.
• D (correct): Moment is F times perpendicular distance: 35 N × 0.20 m = 7 N·m.

Answer: D

Correct answer: 160 N. The torque relation

can be rearranged to find any one quantity. To get force, divide torque by the arm length:

Because the arm is only a quarter meter, the force must be four times the torque value. Check by multiplying back: 160 N × 0.25 m = 40 N·m. Inverting the division gives a tiny force that cannot be right.

• A: Ten newtons would produce just 2.5 N·m on the stated arm.
• B: Dividing the arm length by the torque (0.25/40) inverts the relationship F = T/r.
• C: Adding numeric torque and arm length is dimensionally invalid.
• D (correct): Rearranging T = F r gives F = 40/0.25 = 160 N.

Answer: A

Correct answer: 5 N·m. Only the part of a force perpendicular to the lever arm creates rotation. When a force acts at an angle θ to the handle, that perpendicular part is F sin θ, and sin 30° = 0.5. So torque is

N·m, half of the 10 N·m a perpendicular push would give. Ignoring the angle is the usual mistake. Torque is zero only when the force points straight along the handle.

• A (correct): Moment is Fr sin θ = 50(0.20)(0.5) = 5 N·m.
• B: Ten N·m assumes the force is perpendicular to the handle.
• C: Fifty N·m does not result from this geometry because both the short lever arm and the sine of the angle matter.
• D: The applied force has a nonzero component perpendicular to the handle at 30 degrees, so torque is not zero.

Answer: B

Correct answer: 6.0 mm. Pitch is the crest spacing, but travel per turn depends on lead. On a double-start thread two helixes run side by side, so lead is twice the pitch:

per turn. Three turns then give

The tempting shortcut of multiplying pitch by turns gives 3.0 mm, which would be correct only for a single-start thread.

• A: A third of a millimeter uses a reciprocal unrelated to screw lead.
• B (correct): Lead is 2 × 1.0 = 2.0 mm/turn, so three turns advance 6.0 mm.
• C: One-and-a-half millimeters divides rather than multiplies by the number of starts.
• D: Three millimeters treats lead as pitch despite two starts.

Answer: A

Correct answer: 6.35 mm. Since 1959 the inch has been defined as exactly 25.4 millimeters, so inch-to-millimeter conversions are exact multiplications. A quarter inch is

A useful memory hook is that 1/4 inch is a little more than 6 mm. The tempting errors are confusing one inch with a quarter inch, or treating a quarter-inch fastener as interchangeable with a 6 mm metric one because the numbers are close.

• A (correct): Multiply 0.25 inch by exactly 25.4 mm/inch to obtain 6.35 mm.
• B: The value 25.4 mm is exactly one full inch; the question asks for only one quarter of that length.
• C: 6.00 mm is close to M6 but is not the actual quarter-inch conversion.
• D: 2.54 mm equals one tenth inch, not one quarter inch.

Answer: B

Correct answer: Similar outside diameters do not establish thread compatibility. A 1/4-inch Unified thread measures about 6.35 mm and an M6 thread is 6.0 mm, so they look nearly the same with a caliper. Yet they belong to different systems with different pitches; 1/4-20 has about 1.27 mm pitch versus 1.0 mm for coarse M6. Forcing one into the other cross-threads and damages parts. Confirm compatibility with a thread pitch gauge and the parts specification, not diameter alone.

• A: Nuts should not be interchanged without full thread matching.
• B (correct): A quarter-inch nominal diameter and M6 designation can be numerically close but use different thread systems and pitches.
• C: Strength grades belong to specific materials and grading systems, so similar diameter readings cannot establish equivalent strength.
• D: Pitch cannot be inferred from proximity of outside diameters.

Answer: B

Correct answer: 10 N·m. The short-form torque equation estimates the torque needed for a target preload: T ≈ K × F × d, where K is a nut factor reflecting friction, F is preload and d is nominal diameter. With consistent units,

N·m. Most mistakes here are decimal slips, giving 1 or 100. K varies with lubrication and finish, so actual service values come from the manufacturer.

• A: 100 N·m is ten times the calculated illustrative value.
• B (correct): Multiply the supplied factors: 0.20 × 5000 × 0.010 = 10 N·m; this is a model, not a universal service torque.
• C: One newton-meter is a factor of ten too small for the numerical product of K, preload, and nominal diameter.
• D: 1000 N·m omits the small nominal diameter factor in the multiplication.

Answer: A

Correct answer: Use a manufacturer-approved repair or replacement procedure. A threaded hole holds a joint by the shape and strength of its thread flanks. Once those are damaged, the safe options are a method the manufacturer approves, such as a thread insert, a specified oversize repair, or replacing the part. Shortcuts like hammering, guessing at a larger bolt, or gluing a loose bolt may seem to hold but leave unknown strength. In critical assemblies, a hidden weak joint can fail under load.

• A (correct): Thread repair must restore verified geometry and strength through an approved insert or other specified method, or replacement.
• B: Hammering an engaged fastener creates uncontrolled damage and cannot verify capacity.
• C: Oversizing an engineered hole can damage the housing or create new failure modes.
• D: Adhesive may help prevent unscrewing but cannot restore missing metallic thread flanks needed to sustain the designed joint load.

Answer: B

Correct answer: Certain dissimilar metals in contact with an electrolyte. Galvanic corrosion works like a battery: two metals with different electrical potentials, joined electrically and wet with an electrolyte such as salt water, form a cell. The less noble metal, such as aluminum or zinc, corrodes faster while the more noble one, such as stainless steel, is protected. Remove any part of that setup, by keeping it dry, using the same metal, or insulating the joint, and the risk drops.

• A: Proper mechanical socket contact in a dry assembly is not the relevant corrosion mechanism.
• B (correct): Galvanic action generally needs electrochemical potential differences and a conductive path such as a wet electrolyte.
• C: Brief dry inspection with a pitch gauge does not establish an electrochemical cell.
• D: Dry controlled storage eliminates the key electrolyte in this comparison.

Answer: C

Correct answer: 7.5 N·m. Only the part of the force perpendicular to the handle turns the bolt:

• A: This ignores the angle and treats the push as fully perpendicular to the handle.
• B: This uses cos 30 degrees (about 0.87) instead of sin 30 degrees for the perpendicular part of the force.
• C (correct): Multiplying 60 N by 0.25 m by sin 30 degrees (0.5) gives 7.5 N·m.
• D: This divides the force by the arm length instead of multiplying them.

Answer: D

Correct answer: Lag screw. A lag screw is a heavy, usually hex-headed screw that threads into wood (or an approved anchor) instead of taking a nut. It is often called a lag bolt, but it is installed like a screw.

• A: Machine screws have machine threads made to mate with a nut or tapped hole, not wood fibers.
• B: The question states no nuts are used, so this is not a bolt-and-nut assembly.
• C: A blind rivet is a non-threaded permanent fastener for thin sheet, not a hex-head screw driven into a beam.
• D (correct): A heavy hex-head screw that grips wood directly through a pilot hole, with no nut, is a lag screw.

Answer: C

Correct answer: The drive style in the head. These names identify the drive recess, which determines the tool that turns the screw. They say nothing about the thread or the material the screw is made to fasten.

• A: Pitch is given as a distance (mm) or as threads per inch, not by a drive name.
• B: Strength is shown by grade or property class markings, not by the drive recess.
• C (correct): Phillips, Torx and slotted name the shape of the recess that the driver fits into.
• D: The same drive recess appears on both wood screws and machine screws.

Answer: C

Correct answer: 12 mm. For a multiple-start thread, lead equals the number of starts times the pitch:

per turn. Over 5 turns the travel is

• A: This uses the 0.8-mm pitch as the travel per turn, which is only true for a single-start thread.
• B: This is the lead for one turn; it was not multiplied by the 5 turns.
• C (correct): Lead is 3 x 0.8 = 2.4 mm per turn, and 5 turns give 12 mm.
• D: This adds the number of starts to the pitch (3 + 0.8) instead of multiplying them.

Answer: D

Correct answer: 6.5 turns. 13 TPI means each turn advances the nut 1/13 inch. The number of turns is the distance times the threads per inch:

• A: Thirteen turns would advance the nut a full inch, twice the required distance.
• B: This divides 13 by 0.5 instead of multiplying, giving four times the correct count.
• C: This divides 0.5 by 13, which gives a distance-like number, not the turns needed.
• D (correct): Half an inch at 13 threads per inch requires 0.5 x 13 = 6.5 turns.

Answer: A

Correct answer: 360 N. Torque depends on the actual lever arm, which is where the hand pushes: 0.25 m. Rearranging

• A (correct): With the hand 0.25 m from the bolt, 90 N·m divided by 0.25 m requires 360 N.
• B: This uses the full 0.30-m wrench length, but the effective arm is only where the force is applied.
• C: This multiplies torque by the arm length instead of dividing.
• D: This multiplies 90 by the 0.30-m wrench length, which uses both the wrong operation and the wrong arm.

Answer: D

Correct answer: 10,000 N. Solve for F:

The denominator is

Remember the model is only illustrative, because friction changes K.

• A: This divides 24 by 0.012 and leaves out the nut factor K.
• B: This converts 12 mm to 0.12 m instead of 0.012 m, making the result ten times too small.
• C: This multiplies T, K and d together instead of dividing T by K times d.
• D (correct): 24 divided by (0.20 x 0.012 = 0.0024) gives 10,000 N.

Answer: B

Correct answer: Studs left installed in the housing, with nuts holding the cover. A stud is threaded into the housing and left in place. The cover is removed by unscrewing nuts from the exposed stud ends, so the housing threads are not worked each time the cover comes off.

• A: Cap screws still thread in and out of the housing each service, so the wear continues.
• B (correct): The studs stay put, and only the nuts are removed, so the housing's internal threads see little repeated wear.
• C: Lock washers do not change how often the housing threads are engaged and removed, so the wear continues.
• D: Adhesive resists loosening but does nothing to protect the housing threads from repeated removal and reinstallation.

Answer: A

Correct answer: The M12 x 1.25 bolt has finer, more closely spaced threads. Both have a 12-mm nominal major diameter, but the second number is the pitch in millimeters. The 1.25-mm pitch places the threads closer together, so it is the finer thread, and a nut made for one will not properly fit the other.

• A (correct): Its 1.25-mm crest-to-crest distance is smaller than 1.75 mm, which makes it the finer thread.
• B: A larger pitch means threads are farther apart, so there are fewer per millimeter.
• C: Matching diameter is not enough; the pitches differ, so one nut cannot properly mate with both.
• D: Fine thread alone does not make a fastener stronger; material, grade and joint design decide strength.

Answer: B

Correct answer: Tapped holes. Since the screws engage the housing itself, the housing holes must carry internal threads. Those are tapped holes, cut or formed with a tap.

• A: Clearance holes let a bolt pass through without engaging the wall, which would require a nut.
• B (correct): Tapped holes have internal threads, so the screws can thread straight into the housing.
• C: A countersink shapes the hole's top for a flush head but adds no threads for the screw to grip.
• D: Dowel pins locate parts; they leave no threaded hole for the screws.

Answer: B

Correct answer: 9.525 mm diameter, about 1.058 mm pitch. The diameter is 3/8 inch:

The 24 is threads per inch, so the pitch is 1/24 inch: $25.4/24\approx 1.058$ mm.

• A: The diameter is right, but 24 is a count of threads per inch, not a pitch length.
• B (correct): 3/8 inch times 25.4 gives 9.525 mm, and 25.4 mm divided by 24 threads gives about 1.058 mm.
• C: This reads the 3/8 as 3.8 mm and treats the thread count as a length, two unit errors.
• D: These are the inch values (0.375 in and 1/24 in) labeled as millimeters without conversion.

Answer: A

Correct answer: A hex key that fits inside the head. A socket head has an internal hexagon recess, so it is driven with a hex key (Allen key) or a hex bit inserted into the head.

• A (correct): The socket head has an internal hex recess that accepts a hex key or hex bit.
• B: The outside of a socket head is round, so a wrench has no flats to grip.
• C: A flat blade fits a slotted head, not an internal hex recess.
• D: Gripping the threads would damage them and is not how any cap screw is driven.

Answer: B

Correct answer: Decline, because the two marking systems differ and the threads would not match. ISO property classes and SAE grades are separate rating systems, so similar numbers do not make them equivalent. The replacement must match the specified thread designation and the required strength, which an inch bolt cannot do in a metric hole.

• A: Strength ratings cannot be compared by the number alone, and the thread mismatch rules out the swap anyway.
• B (correct): Class 8.8 and Grade 8 come from different standards, and an inch thread will not mate with metric threads.
• C: Wrench size says nothing about thread pitch, diameter or strength class.
• D: A washer cannot correct a thread mismatch or a different strength rating.

Answer: D

Correct answer: Snug all bolts lightly in a crisscross pattern, then bring them to final torque in the same pattern. Tightening in stages using an alternating, crisscross pattern pulls the cover down evenly and keeps the gasket from being crushed on one side. Always use the manual's sequence and torque values when they are given.

• A: Bringing each bolt to full torque one at a time, even in a neat circular order, can warp the cover and crush the gasket unevenly.
• B: Clamping one end first pinches the gasket and can leave a gap at the other end.
• C: An impact wrench does not give controlled, even torque, and a single pass skips the staged snugging that seats the gasket evenly.
• D (correct): Staged, alternating tightening spreads clamping pressure evenly across the gasket.

Answer: A

Correct answer: Galling between the stainless surfaces. Similar stainless steel parts can gall: their surfaces stick and tear under sliding pressure, causing rapid seizure. Since the parts were clean and correctly matched, galling is the best explanation, and the safe action is to stop rather than apply more force.

• A (correct): Sliding stainless surfaces can adhere and tear, producing sudden seizure even with matched, clean threads.
• B: Both parts are stainless steel, and galvanic corrosion develops over time, not during installation.
• C: Low torque does not tear threads; the problem is rising resistance during installation.
• D: Matched left-hand threads install normally, and nothing prevents stainless parts from having them.