Outside, inside and odd-leg calipers and the divider – what each one measures or marks.
Calipers are indirect measuring tools: they take the size from the job, then the size is read on a steel rule. They are made of carbon steel and their legs are hardened at the tips.
Types by joint
- Firm joint calipers – legs held by friction of a rivet joint.
- Spring joint calipers – legs held by a spring and set with a nut; setting does not slip.
Types by use
| Tool | Use |
|---|---|
| Outside caliper | Outside diameter, thickness – legs bent inward. |
| Inside caliper | Bore diameter, width of slots – legs bent outward. |
| Odd-leg caliper (Jenny) | One bent leg, one pointed leg: marks lines parallel to an edge and finds the centre of round bars. |
| Divider | Both legs pointed: scribes circles and arcs, transfers and divides distances. |
Correct "feel" The caliper should just touch the job and pass over it with light pressure. Do not force it – the legs will spring and give a wrong size.
Size of a caliper or divider is the distance from the centre of the joint (pivot) to the tip of the leg.
Quick Revision
- Calipers transfer size; read it on a steel rule.
- Outside → OD, inside → bore, odd-leg → parallel lines/centre, divider → circles.
- Spring joint calipers hold their setting best.
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