Typically, what is the accuracy of a thickness/feeler gage?

Typically, what is the accuracy of a thickness/feeler gage?

Most that I have seen have the presumed thickness on the gage or on the box it is in. If a set like one might buy atSears for spark plugs, then each blade will have the thickness on it.

Hope this helps.

Hershal

Typically, what is the accuracy of a thickness/feeler gage?
If you're referring to size tolerance, it varies with the nominal size (and is usually proportional to the price of the gage). For example, a .250" nominal feeler gage with a tolerance of +/- .0005 would probably be considered acceptable under most circumstances, but that would equal 1/3 of the size of a .0015" feeler.

Typically, what is the accuracy of a thickness/feeler gage?

Some anecdotal evidence: I measured the leaves of the 3 "standard" mechanic's sets I have in my tool boxes using a digi-mic with a resolution of 0.000 05" and an overall uncertainty of better than 0.0001". The Craftsman and Williams sets both read either nominal or one count oversize (0.000 05") on each leaf. The Mitutoyo set read nominal or one count under on each leaf. Since the micrometer reads almost always exactly nominal when measuring gage blocks, it would appear my feeler gauges are manufactured to "within a tenth." The accuracy of these three sets matches my memory of feeler gauges from my days (well past) working as a mill-wright (outside machinist). Most leaf type feeler gauges are cut from ground shim stock and are about as good as shop or grade B gage blocks.

OTOH, If you mean by "accuracy" something like "how accurate can one measure with feeler gauges"; that is dependant upon technique, material, and geometry being measured. When used against spring loaded or gravity loaded surfaces (i.e. valve train of a car or gap under the foot of an unbolted machine), they can be off by an order of magnitude. However, when used by good hands in clean, rigid applications with well defined corners, the measurement result can be amazingly good. Especially considering the price of the instrument (usually under $10).

Try setting a gap with a micrometer and measuring the gap with feeler gages. (Be careful not to press the leaves forcefully into the gap or you will simply deflect the frame of the micrometer.) Next change the gap by 1 division and try again. Then, split the gap between the two divisions just measured and try again. With only a small amount of care, one can distinguish a 1/4 thou (0.000 25") change in the gap with gages of nominal 0.001" steps.

If you need a tolerance or purchasing spec, I dimly recall seeing a federal standard for shim stock and feeler gauges. A search might turn it up.

Galen