Anatomy
Parts of a vernier caliper
Twelve parts make up the instrument. Explore mode in the simulator labels each one on the drawing; the table below is the same information in reference form.
| # | Part | Function |
|---|---|---|
| 1 | Fixed jaw | Forged in one piece with the beam. Because it never moves, its measuring face defines the zero for every reading you take. |
| 2 | Sliding jaw | The moving assembly. It carries the vernier scale, the depth rod, the thumb roller and the locking screw as one unit. |
| 3 | Outside jaws | The lower pair. Their inner faces measure external sizes — shaft diameters, bar widths, plate thicknesses. |
| 4 | Inside jaws (nibs) | The upper knife edges. Their outer faces measure internal sizes. You open them inside a hole rather than closing them onto it. |
| 5 | Main scale beam | The rigid graduated blade. It keeps both jaws parallel and carries the millimetre graduations. |
| 6 | Metric graduations | One millimetre per division. The last whole division to the left of the vernier zero gives the main scale reading. |
| 7 | Imperial scale | The upper edge is graduated in 0.025 in steps, with its own 25-division vernier on the slider giving 0.001 in. It is engraved alongside the millimetre scale, not instead of it — switch Units to read the instrument in inches. |
| 8 | Vernier scale | The auxiliary sliding scale. Its divisions are deliberately shorter than the main scale divisions, and that shortfall is the least count. |
| 9 | Vernier zero line | In line with the sliding jaw face. It marks the main scale reading, and reveals a zero error when the jaws are closed. |
| 10 | Depth rod | Slides out of the tail of the beam by exactly the jaw opening, so it measures depths on the same scale. |
| 11 | Thumb roller | Sets a consistent, repeatable contact pressure. Using it rather than squeezing the jaws is what stops you compressing soft parts. |
| 12 | Locking screw | Clamps the sliding head so the setting cannot drift while you withdraw the caliper and read it. |
References
Standards
The graduations, geometry and accuracy classes simulated here follow the standards that govern real vernier instruments. Cite these when specifying a caliper or writing up a lab report.
- ISO 13385-1Dimensional measuring equipment — CallipersDefines design requirements and the maximum permissible errors at different measuring lengths.
- ASME B89.1.14CalipersThe US standard covering accuracy, repeatability and calibration for vernier, dial and digital calipers.
- BS 887Precision vernier callipersThe British Standard still referenced across UK and Commonwealth technical syllabi.
- DIN 862Vernier callipersThe German equivalent, widely cited on European manufacturers’ calibration certificates.
Try it
Everything on this page is easier to believe with the instrument in front of you.
The simulator has draggable jaws, three least counts, imperial mode, zero-error simulation and a practice mode that marks your readings.
Open the caliper simulatorKeep reading
How to read a vernier caliper
The five steps, the TR = MSR + (VSR × LC) formula worked through, and the six mistakes that spoil a reading.
Least count
Where 0.02 mm comes from, a table of every common vernier, and the four jobs a caliper is the wrong instrument for.
Zero error
The fault that adds itself to every reading you take, why it is invisible in the results, and how to correct for it.
Frequently asked questions
Short answers to the questions that come up most often about reading and using a caliper.