Use of Hand Tools, Measuring Instruments, and Test Equipment
Domain 2 tests whether you can choose the right instrument, verify it, read it correctly and care for it. Expect tool identification, instrument resolution, zero and calibration checks, and correct use of test equipment.
Core rules
- Torque wrench: click-type is accurate from roughly 20% to 100% of its range; store at the lowest setting; never use it to loosen a fastener; tighten in the maker's sequence, usually spiral from the centre, in steps.
- Torque-to-yield (TTY) bolts must be replaced and final-tightened by angle, not torque, because the shank has already stretched into its plastic range.
- Feeler gauge for valve clearance, spark plug gap and ring end gap; vernier caliper resolution 0.02 mm; outside micrometer 0.01 mm; dial indicator with magnetic base for runout, backlash and end play; plastigauge for bearing oil clearance; bore gauge for taper and out-of-round.
- Zero-check calipers and micrometers before use and clean the anvils - grit reads as wear.
- Multimeter: never measure resistance or continuity on a live circuit; select a range above the expected value; use diode/continuity mode for harness checks.
- Hydrometer or refractometer for battery electrolyte and coolant concentration.
Worked example
A micrometer shows 7.5 mm on the barrel and 22 on the thimble. The reading is 7.5 + (22 × 0.01) = 7.72 mm; the barrel carries whole and half millimetres, the thimble adds hundredths. Measuring the same bore at top, middle and bottom in two axes gives taper and out-of-round. If the bore limit is 76.00–76.03 mm and one axis reads 76.11 mm, the cylinder needs boring or replacement, not just new rings - the wear is in the bore, not the ring. Always take several readings and average before condemning a part.
Traps
- Reading a caliper at an angle (parallax) or measuring a hot component.
- Using an adjustable wrench on brake line flare nuts and rounding them.
- Forcing a caliper closed, or using outside jaws for an inside measurement when inside jaws exist.
- Forgetting to preload a dial indicator, so runout reads low.