Plug and Pin Gages

Plug and pin gauges are used to compare hole and slot dimensions or locations to specific tolerances. There are several basic types of products. Go gauges and no-go gauges are fixed limit gauges with gauging limits based on the plus or minus tolerances of inspected parts.  Go gauge dimensions are based on the minimum inside diameter (ID) tolerance of the inspected part. No-go gauge dimensions are based on the minimum outside diameter (OD) tolerance of the inspected part. Double-ended go/no-go gauges include a go gauge pin on one end of a handle and a no-go gauge pin on the opposite end. Progressive or step go/no-go gauges have stepped pins with the go gauge surface and the no-go gauge surface on the same side of the handle. Master gauge blocks, master or setting discs, and setting rings are master gauges used to calibrate or set working plug or pin gauges. Working devices are used for dimensional inspection and checked periodically against a master gauge. Annular plug gauges are large, usually over 8” in diameter, and used to set or check micrometer or other OD gauges. Some plug and pin gauges have internal or external threads for gauging threads parts or part features. Others are packaged in a kit with adjustment tools such as alternate extensions and contact tips, holders, and bases.

Plug and pin gauges use several different gauging technologies. Pneumatic systems measure the changes in flow or pressure in air nozzles or inlets located inside air plugs, rings, or snaps. Pneumatic comparators, digital readouts, analog amplifiers, columns, and flowmeter/rotameter tubes are used to display dimensional data. Electronic gauges use linear variable differential transformers (LVDTs), capacitive, inductive or other electronic probes to sense the distance of displacement of a contact or stylus. Mechanical gauges use comparison or the physical movement and displacement of a gauging element (e.g., spindle, slide, stem) to determine the dimensions of a part or feature.  Micrometers, calipers, indicators, plug gauges, ring gauges or snap gauges are examples of mechanical gauges. These devices may use an integral electronic probe in addition to the mechanical gauging elements. 

There are several geometries and holder/handle types for plug and pin gauges. Cylindrical plug and pin gauges have a tubular shape and no taper. Tapered devices have a conical form. Pin and plug gauges with ball-shaped ends are used to gauge spherical cavities and tapered holes. Hex or nut gauges have hexagonal or square cross- sections for gauging countersunk holes that lock nut or bolt heads in place during fastening. Plain gauges with smoother outer surfaces and bores are also available. There are three holder/handle mounting types. Taperlock gauges fit a tapered cavity in the handle. Trilock gauges have a central hole for a fastener that attaches the gauge to the handle. Reversible gauges allowing both ends of a gauge to be used. When one end becomes worn, the gauge is reversed in the holder. Some devices have heat-insulating, plastic handles.   

Specifications for plug and pin gauges include plug size or diameter, set range, and set steps or increments. Suppliers specify products according to metric or English (imperial) measurements. Tolerance class is an important consideration. Class XX gauges range in size from .001" to 0.08250" and have a tolerance of no more than 0.00002". Class X gauges range in size from .001" to 0.08250" and have a tolerance of no more than 0.00004". Class Y gauges range in size from .001" to 0.08250" and have a tolerance of no more than 0.00007". Class Z gauges range in size from .001" to 0.08250" and have a tolerance of no more than 0.0001".

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