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How to Use Outside and Inside Spring Calipers

Guide · Updated October 28, 2026

Spring calipers have no scale. They are transfer tools: set them to a part or a micrometer, then compare or measure the setting. With practice they are surprisingly repeatable, and they reach into places a micrometer cannot.

Check against a standard

Set or check calipers against a micrometer or a gage block. The free Gage Block Calculator builds the stack.

Step by step

  1. Pick the type: Outside calipers have legs bowed inward for shafts; inside calipers have legs turned outward for bores.
  2. Set roughly: Open with the nut to a little over size.
  3. Find the feel: Hold the caliper lightly by the bow; the legs should just drag over the part under their own weight.
  4. Adjust: Turn the nut in small steps until you get that drag.
  5. Transfer: Measure the setting with a mic: hold one leg on the anvil and feel for the same drag over the spindle.
  6. Compare: Or set from a mic and compare parts against the setting.
  7. Square the legs: Keep the caliper square to the axis, not tilted.

Worked example: turning to a size on the lathe

You need a 1.250 in shaft. Set the outside caliper on a micrometer locked at 1.250 in until it drags lightly. Stop the lathe and try the caliper on the work: if it will not pass, take another cut. Turn to within a few thousandths, then finish with the micrometer. Spring calipers are a transfer tool: with good feel they usually repeat within a few thousandths, not tenths.

Worked example: inside caliper to a mic

Set the inside caliper in a bore until one leg pivots on the wall and the other just drags across the far side. Move it to an outside mic and close the mic until the same drag is felt. If the mic reads 0.7505 in, the bore is about 0.750 in. Rock across the diameter to find the maximum; tilting along the bore reads a chord, which is shorter.

Why feel matters

Spring calipers flex. A heavy hand opens the legs and reads big on outside work. Hold the caliper by the spring, not the legs, and use the same light touch every time.

Where they beat a mic

In grooves and behind shoulders where a mic frame will not fit, and for checking long work on the lathe without removing it.

Common problems

Setting moves: nut loose or bumped; recheck before each use. Reads big: forcing the legs. Reads small in a bore: caliper tilted across a chord. Inconsistent between people: different feel; use a mic for anything tighter than a few thousandths.

Tips

FAQ

Do spring calipers have a scale?

No; they transfer a size to a rule or mic.

How accurate are they?

With good feel, a few thousandths.

How do I set them?

From a mic or gage block with a light drag.

Outside vs inside?

Outside for shafts, inside for bores.

Why do readings vary?

Different pressure; keep the touch light.

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