Tools
Hand and power tools; precision measuring with the micrometer, vernier caliper and dial gauge; go/no-go gauging, torque wrenches and instrument care.
Tools — summary notes
Free- Covers hand tools, power tools and precision measuring equipment, together with their correct use, care and calibration.
- The micrometer measures to 0.01 mm: the sleeve gives whole and half millimetres, the thimble the hundredths. It has a ratchet or friction thimble so the measuring pressure is consistent — over-tightening distorts the frame and the reading.
- The vernier caliper measures external, internal and depth dimensions; the vernier scale resolves the fraction of a main-scale division, typically to 0.02 mm.
- The dial test indicator measures run-out, end-float and backlash by comparison rather than absolute size, and must be rigidly mounted to be meaningful.
- Go/no-go gauges give a rapid pass/fail against limits without reading a value — the GO end must enter, the NO-GO end must not.
- Torque wrenches must be set to the specified value, pulled smoothly at the handle centre, and returned to their lowest setting for storage so the spring does not take a set.
- Precision instruments are stored clean, dry and separated, never loose in a toolbox, and are checked for zero error before use.
- ⚠ Exam trap: the micrometer's ratchet exists to standardise the measuring FORCE, not to speed it up; and a dial gauge reads a difference, not a dimension.
- Micrometer resolution
- typically 0.01 mm — sleeve (mm and ½ mm) + thimble (0.01 mm)
- Vernier resolution
- typically 0.02 mm
- Go / no-go
- GO must enter · NO-GO must not
A micrometer reads 7.5 mm on the sleeve with the thimble showing 23. What is the measurement?
7.5 mm from the sleeve plus 0.23 mm from the thimble gives 7.73 mm. The half-millimetre mark on the sleeve is the commonest thing to overlook.
Why is a torque wrench wound back to its lowest setting before being put away?
A click-type wrench holds its setting with a spring under compression. Leaving it wound up lets the spring take a permanent set, so the wrench gradually reads high and applies less torque than indicated.
Tools concept map
FreeTools
Tools quiz
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