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How to Set a Snap Gage

Guide · Updated October 27, 2026

An adjustable snap gage checks outside diameters and thicknesses on a pass/fail basis. The go anvil is set to the maximum size and the no-go anvil to the minimum. Gage block stacks are the standard way to set both.

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Step by step

Build the stacks: Wring stacks at the maximum (go) and minimum (no-go) sizes. The free Gage Block Calculator finds the fewest blocks.
Set the go anvil: Adjust until the go stack passes with a light, even feel under the gage's own weight.
Set the no-go anvil: Adjust until the no-go stack just doesn't pass.
Lock and seal: Tighten the locks, then re-check both stacks.
Use it correctly: Let the gage pass over the part under its own weight. Don't force it.

Checking the setting

Re-check both anvils on the blocks at the start of every shift.
Look for wear on the go anvil, since it takes most of the contact.

Worked example: setting a 1.0000 in GO/NO-GO snap gage

A shaft is drawn at 1.0000 in +0.0000/−0.0010, so the GO anvil is set at the maximum material size, 1.0000 in, and the NO-GO anvil at the minimum, 0.9990 in. Wring a 1.0000 in block (or a 0.500 + 0.500 stack) and set the GO anvil so the block passes under its own weight with a light drag. For NO-GO, build 0.9990 in from a 0.149 + 0.850 stack and set the second anvil so that stack just passes. A part at 0.9995 in then passes GO and stops at NO-GO, as it should.

Gage makers normally apply a small wear allowance and gage tolerance inside the part limits so a worn gage never accepts a bad part. A common shop rule is to keep total gage tolerance near 10% of the part tolerance; on a 0.0010 in band that is 0.0001 in. Recheck the setting against the blocks at the start of each shift and whenever the gage is dropped, and lock the anvil screws only after the final check, because tightening can shift the anvil a few tenths.

Fuller worked example: go and no-go for 0.749/0.750 in

For a shaft toleranced 0.749–0.750 in, set the go anvil at 0.7500 in using the single 0.750 in block from an 81-piece set, and the no-go at 0.7490 in using 0.109 + 0.140 + 0.500 = 0.749 in. The go stack should pass the anvils with a light slide; the no-go should just stop.

Check both settings again after locking the anvils, because the lock screws can shift the setting a few tenths. Let the gage and blocks soak to room temperature first.

FAQ

Which side is go on a snap gage?

The go side is set to the part's maximum size and should pass. The no-go side is set to the minimum and should not.

How do you set a snap gage?

Use gage block stacks at the maximum and minimum sizes, adjust each anvil until it gives the right feel, then lock it.

How much force should I use?

Only the gage's own weight. Forcing it springs the frame.

How often do I re-set one?

Check it on blocks every shift and re-set if it has drifted.

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General shop information only — follow your gage manufacturer's instructions and your quality system.