Gauge, MEASURING

Instruments to secure precision in size for manufactured articles. Usually they are pieces of steel hardened, or of wrought-iron case-hardened, of the required shape for the dimension which they are to determine, and carefully ground to exact length, diameter, or caliber, as the case may require. The dimension is tested on a comparator to prove its agreement with a standard unit. There are also limit gauges which are a given number of thousandths of an inch larger and smaller than the standards; the size of the measured piece must be smaller than the superior limit and greater than the inferior. There are also thread gauges for screws. Gauges are used also to set CALIPERS (q. v.) by, instead of depending on the ordinary machinists' scales for work at lathes, etc.