Tools
Measuring and applying force
Hand tools and measuring instruments are examined as much for their limitations as for their use. Know the common measuring tools and their resolution: steel rule (0.5 mm), vernier caliper (typically 0.02 mm), micrometer (0.01 mm), dial test indicator (0.01 mm or finer), feeler gauges for gaps and clearances, go/no-go gauges for quick acceptance checks, and depth and bore gauges. Know how to read a micrometer that has a zero error and how to correct for it, how to use a DTI for runout and concentricity, and why instruments carry a calibration label and are checked on a schedule.
Know the torque wrench family: click-type, break-back, beam or deflecting, and torque multipliers for high values. Store at the lowest setting, use to tighten only, support the head squarely, and re-check calibration after a drop or overload.
Know the correct tool for the fastener: correct size and type of spanner (open, ring, socket, flare-nut for pipe unions, crowfoot), six-point sockets for damaged heads, screwdrivers matched to the slot, and never an adjustable wrench on a tight or critical fastener. Punches, chisels and drifts must be free of mushroom heads; files need handles; pullers must pull squarely and never be hammered.
Traps: reading a vernier from the wrong scale line, expecting torque to stay correct with an extension bar, confusing metric and imperial spanner sizes, and using a calibrated instrument outside its range.
Rule of thumb: a measuring tool is only as good as its calibration label and its zero check - verify zero before you trust the number.