WTMA Common Tools and Fasteners 4 — Questions and Answers
Question 1: What distinguishes a machine screw from a wood screw?
- Machine screws have a tapered shank and coarser threads
- Machine screws have uniform threads designed to mate with nuts or tapped holes (Correct answer)
- Machine screws are always larger in diameter
- Machine screws have a self-drilling tip
Correct answer: Machine screws have uniform threads designed to mate with nuts or tapped holes
Machine screws have uniform (non-tapered) threads designed to thread into nuts or pre-tapped metal holes, unlike wood screws which have tapered shanks for wood.
Question 2: Which wrench type is least likely to damage a soft or rounded fastener head?
- Open-end wrench
- Adjustable wrench
- Box-end (ring) wrench (Correct answer)
- Pipe wrench
Correct answer: Box-end (ring) wrench
A box-end wrench surrounds all six sides of the hex fastener, distributing force evenly and reducing the chance of rounding the corners.
Question 3: What is a 'UNC' thread designation in the US fastener system?
- Ultra-narrow coarse thread
- Unified National Coarse thread (Correct answer)
- Universal non-corrosive thread
- Unified National Cylindrical thread
Correct answer: Unified National Coarse thread
UNC stands for Unified National Coarse, a standard thread series with fewer threads per inch than UNF (fine) threads.
Question 4: A snap ring (circlip) is used in an assembly. What is its function?
- Seal against oil leakage
- Retain a component on a shaft or in a bore (Correct answer)
- Provide electrical grounding
- Reduce vibration between parts
Correct answer: Retain a component on a shaft or in a bore
Snap rings (circlips) seat in grooves on shafts or in bores to axially retain components like bearings, gears, or pins.
Question 5: Which tool is used to apply a precise, measured amount of torque to a fastener?
- Breaker bar
- Torque wrench (Correct answer)
- Speed handle
- Extension bar
Correct answer: Torque wrench
A torque wrench is calibrated to apply and measure a specific torque (twisting force) to ensure proper fastener tension.
Question 6: What is the advantage of a self-tapping screw in sheet metal assembly?
- It requires a pre-drilled and tapped hole
- It cuts its own threads as it is driven, eliminating separate tapping (Correct answer)
- It never requires a pilot hole
- It can be torqued to higher values than machine screws
Correct answer: It cuts its own threads as it is driven, eliminating separate tapping
Self-tapping screws form or cut their own mating threads as they are driven into a pre-drilled pilot hole, eliminating the need for a separate tapping step.
Question 7: When filing metal, which stroke actually removes material — the push stroke or the pull stroke?
- Pull stroke only
- Push stroke only (Correct answer)
- Both strokes equally
- Neither; only oscillation removes material
Correct answer: Push stroke only
Metal files are designed with cutting teeth angled to cut on the push (forward) stroke; the pull stroke rides over the work without cutting.
WTMA Common Tools and Fasteners 4
What distinguishes a machine screw from a wood screw?