A simple caliper is used with a scale to measure diameters. Outside calipers are bowlegged to measure outside diameters; inside calipers used for inside diameters have straight legs with the feet turned outward. Calipers are adjusted by pulling or pushing the legs to open or close them. Additionally, fine adjustment is made by tapping one leg slightly on a hard surface to close them or by turning them upside down and tapping on the joint end to open them.
Spring-joint calipers have the legs joined by a strong spring hinge and linked together by a screw and adjusting nut. Transfer calipers are available to measure chamfered cavities (grooves) or for use over flanges. They are equipped with a small auxiliary leaf is locked to the leg.