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Feeler Gage Basics

Guide · Updated October 27, 2026

Feeler gages measure gaps: tool setting, machine gib and way clearances, part fit, valve lash. They're simple but feel-dependent, so a few habits make the difference between a guess and a measurement.

Wider gaps? Use blocks

If a block fits the gap, a gage block stack is far more accurate. Build it with the free Gage Block Calculator. Free, no login.

Step by step

Clean the leaf and the gap: Wipe oil and grit off the leaf and out of the gap.
Start small: Try a leaf that slides freely, then step up in size.
Find the drag: The correct leaf has a light, even drag. The next size up won't enter without force.
Stack if needed: Stack the fewest leaves that make the size.
Wipe and store: Wipe, lightly oil and close the set after use.

Getting a consistent feel

Hold the leaf flat to the gap, never at an angle.
Check the drag against a known gap, such as two gage blocks with a known difference.
Have one person do the measuring when results matter.

Keeping leaves accurate

Mic leaves on a micrometer checked with gage blocks: how to check a micrometer.
Throw away kinked leaves. A kink adds thickness.
Store them lightly oiled and closed: see storage habits.
For related shop gauges, see pin gages and radius gages.

Worked example: checking a gap with a feeler gage

A cover plate needs a gap checked between its edge and a housing. Wipe the gap and the leaves clean. Try a thin leaf that slides freely, then step up one size at a time. Note the largest leaf that slides in with a light, even drag while the next size up will not enter without force; that leaf is the gap reading. Check at both ends and the middle of the gap, since a taper shows up as different readings. If you need a size between leaves, stack the fewest leaves that make it, then wipe and close the set.

FAQ

How do you use a feeler gage?

Slide a leaf into the gap. The right size drags slightly as it slides, while the next size up won't go in without force. Stack leaves for sizes between leaves.

How accurate are feeler gages?

Good to about ±0.0002 to ±0.0005 in per leaf depending on quality and thickness, and the feel adds more. They're for gaps and clearances, not precision sizing.

How do I check feeler gage leaves?

Mic each leaf with a micrometer that's been checked with gage blocks, at a few spots along its length, and replace bent, kinked or worn leaves.

Can I stack feeler gage leaves?

Yes, but each leaf adds its own error and any kinks add more, so use as few as possible, just like gage blocks.

Can I use gage blocks instead?

For gaps wide enough to take a block, yes, and they're more accurate. Build the size free with the Gage Block Calculator at gageblockcalc.com.

Related guides and calculators

Build your stack in seconds

The free Gage Block Calculator finds the fewest-block combination for inch and metric sets, with wear blocks. No login.

Questions? Ask a machinist.

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