gauges

Gauges are devices or systems used to determine size, quantity, or other physical dimensions. The term covers a wide range of tools and standards across engineering, manufacturing, rail transport, and weaponry, and can denote both an instrument and the scale it reads.

Common categories include measurement gauges (instruments that read a dimension or value) and thickness or bore gauges (used to measure wires, sheets, or bores).

Measurement gauges include pressure gauges, which indicate gas or liquid pressure; vacuum gauges, which measure low-pressure conditions; and dial gauges or dial indicators, which quantify small linear displacements with a rotating dial.

Thickness and bore gauges include American Wire Gauge (AWG), a standard for electrical wire diameter; and sheet-metal gauges, such as Birmingham or similar systems, where higher gauge numbers denote thinner material and the exact thickness varies by material.

Track gauge refers to the distance between the inner faces of the rails of a railway track; standard gauge is 1,435 millimeters, though broad and narrow gauges exist in different regions. Gun gauge is a shotgun bore designation, where higher numbers indicate a smaller bore (for example, 12 gauge).

Gauge blocks are precision-length blocks used to calibrate measuring instruments and set standards in metrology. In manufacturing, gauges serve for inspection, tolerancing, and quality control, and gauge systems are defined by regional standards and industry specifications.