Combo comes with 1pc Inside + 1pc Outside 200MM 8" Firm Joint calliper. A firm joint caliper is a measuring instrument that consists of two adjustable legs or jaws for measuring the dimensions of material parts. 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. In the hands of a skilled worker, firm joint caliper are a valuable measuring tool.