A snap gauge is a form of

go/no go gauge A go/no-go gauge refers to an inspection tool used to check a workpiece against its allowed tolerances via a go/no-go test. Its name is derived from two tests: the check involves the workpiece having to pass one test (''go'') and fail the other ...

. It is a limit

gauge Gauge ( or ) may refer to: Measurement * Gauge (instrument), any of a variety of measuring instruments * Gauge (firearms) * Wire gauge, a measure of the size of a wire ** American wire gauge, a common measure of nonferrous wire diameter, es ...

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.

Details

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 gauges may be machined and ground out of a single block of metal or adjustable snap gauges, 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

gauge blocks Gauge blocks (also known as gage blocks, Johansson gauges, slip gauges, or Jo blocks) are a system for producing precision lengths. The individual gauge block is a metal or ceramic block that has been precision ground and lapped to a specific ...

feeler gauges A feeler gauge is a tool used to measure gap widths. Feeler gauges are mostly used in engineering to measure the clearance between two parts. Description They consist of a number of small lengths of steel of different thicknesses with measureme ...

are sandwiched between two anvils. Adjustable snap gauges 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 gauge is needed. Gauge blocks would typically be used to initially set the width of the measuring aperture(s). A variation is the snap indicator gauge, which incorporates a dial indicator or electronic digital indicator as one of the anvils. This indicator displays the deviation from the preset dimension and the indicator may have high and low tolerance limits marked by means of two extra needles, alteration of the dial face, or programming into an electronic indicator. Another variation adds, in addition to the dial or electronic indicator, a micrometer adjustment on the anvil opposite the indicator anvil. This may be referred to as a snap gauge or an indicating micrometer and may be quickly preset for short runs of parts. Snap gauges facilitate making

interchangeable parts Interchangeable parts are parts ( components) that are identical for practical purposes. They are made to specifications that ensure that they are so nearly identical that they will fit into any assembly of the same type. One such part can freely r ...

. Snap gauges have been in existence and referred to by that name since at least 1898. In a manufacturing plant, snap gauges would normally be re-calibrated at scheduled intervals. Often, snap gauges will be calibrated by skilled workers and used by semi-skilled workers; the snap gauge is faster than a

micrometer Micrometer can mean: * Micrometer (device), used for accurate measurements by means of a calibrated screw * American spelling of micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...

and requires less skill to use correctly. Some vendors who resell a different measuring instrument,

bore gauge A bore gauge is a collective term for the tools that are unique to the process of accurately measuring holes. Transfer gauges Telescopic gauges These are a range of gauges that are used to measure a bore's size, by transferring the internal ...

, muddy the waters by referring to them as snap gauges, unlike the manufacturer who uses the correct nomenclature.Fowler Telescoping Gage product data sheet
Unlike a snap gauge, these measure inside (bore) dimensions, not outside dimensions, and are usually reset for each part measured.

References

{{Metalworking navbox, toolopen Length, distance, or range measuring devices Metalworking measuring instruments