Snap gage

A snap gage is a form of Go/no go gauge. It is a limit gage with permanently or temporarily fixed measurement aperture(s) (gaps) which is used to quickly verify whether an outside dimension of a part matches a preset dimension or falls within predefined tolerances. The surfaces which define the edges of the aperture are the anvils, which may be made of separate pieces of hard material such as tungsten carbide for wear resistance. Two apertures are frequently used to provide Go/No-Go testing and are often arranged such that a part being measured can pass through the two apertures in sequence; a part that is within tolerance will pass through the first maximum size limit aperture but will not be able to pass through the minimum size limit aperture. A snap gauge usually has a "C" shaped frame with the aperture(s) at the opening of the "C". Snap gages may be machined and ground out of a single block of metal or adjustable snap gages, which have movable anvils that may be adjusted over a limited range of sizes, may be used. They may also be of built up construction in which one or more gage blocks or feeler gauges are sandwiched between two anvils. Adjustable snap gages may be reset to compensate for wear or re-tasked for measuring a different dimension and can be purchased off the shelf and set rather than needing to be fabricated from scratch when a new gage is needed. Gauge blocks would typically be used to initially set the width of the measuring aperture(s).