measuring instrument that consists of two adjustable legs or jaws for measuring the dimensions of material parts. The calipers on the right side of the illustration--> have an adjusting screw and nut and are known as spring calipers; those on the left are an illustration of firm-joint calipers, which are held in place by friction at the joint. Outside calipers measure thicknesses and outside diameters of objects; inside calipers measure hole diameters and distances between surfaces. To check the dimensions of a machined part, the calipers are first adjusted to the required dimension on a ruler or a standard plug or hole gauge; accuracy in calipering depends in large part on the sense of touch of the operator.