Outside jawsClose on the outside of an object to measure its width.
Inside jawsOpen inside a hole to measure its inside size.
BeamThe long bar the slider runs along.
SliderCarries the moving jaws, the dial and the lock.
DialShows the fraction of a millimetre or inch past the main scale.
Main scaleThe graduations along the beam, read first.
Depth rod, lock and roller 3
Depth rodSlides out of the end of the beam to measure depths.
Locking screwLocks the slider so a size can be held.
Thumb rollerRolled with the thumb to move the slider finely.
How this list was compiled: Read 2026-09-26. (1) Wikipedia, Calipers, https://en.wikipedia.org/wiki/Calipers : outside large jaws, inside small jaws, depth probe or depth rod, main scale, the retainer (lock), a fixed jaw and another jaw that slides along the scale, the beam, a wheel on some calipers; the dial caliper's rack and pinion turns a pointer on a round dial; its slide can be locked with a small lever or screw. (2) Mitutoyo, Quick Guide to Precision Measuring Instruments, Calipers: Nomenclature, https://www2.mitutoyo.co.jp/eng/pdf/E4329_QuickGuide.pdf : outside jaws, inside jaws, depth bar, beam, slider, locking screw, thumbwheel (thumb-roller), main scale, dial. Licence: own work
The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work
How it works
The parts of a dial caliper on one caliper, face-on. Start with the 6 main parts, then the depth rod, the locking screw and the thumb roller.
Read the full guide
Three ways to measure
The outside jaws close on the outside of an object; the inside jaws open inside a hole; the depth rod slides out of the end of the beam into a hole to measure its depth. All three move together with the slider.
Reading it
Read the main scale along the beam at the slider's edge, then add the dial's reading. Roll the thumb roller to close the jaws gently, and tighten the locking screw to hold a size.
A dial caliper and a vernier caliper share the jaws, beam and main scale; the dial replaces the vernier scale.
Questions and answers
What are the parts of a dial caliper?
The outside jaws, inside jaws, beam, main scale, slider, dial, locking screw, thumb roller and depth rod.
What is the depth rod on a caliper?
A thin rod that slides out of the end of the beam as the jaws open, to measure the depth of a hole or step.
How does the dial on a caliper work?
A small rack and pinion turns a pointer round the dial as the slider moves, so you read the final fraction directly without a vernier scale.