caliper

A caliper is a measuring instrument used to determine the dimensions of an object with a high degree of accuracy. Most calipers have a pair of jaws that move along a marked beam to measure external dimensions, internal dimensions, or depth. The term covers several variants that range from simple sliding devices to advanced digital readouts.

Common types include outside calipers for measuring external dimensions, inside calipers for internal dimensions, and depth calipers with a rod extending from the end. Modern calipers are available in vernier, dial, and digital formats. Some models provide both metric and imperial scales and may include a depth rod for measuring depths in holes or recesses.

Operation involves placing the caliper around or into the object and adjusting the sliding jaw until it just touches the surfaces being measured. Readings can come from the main scale and a secondary scale (vernier or dial) or from a digital display. Accurate use requires zeroing the instrument with the jaws closed and keeping the measuring surfaces clean and free from burrs or debris.

Applications span metalworking, machining, automotive, woodworking, and scientific laboratories. Calipers are used to measure thicknesses, diameters, and depths, to verify tolerances, or to transfer precise measurements to other tools.

Care and maintenance include keeping the instrument clean, avoiding exposure to harsh chemicals, and storing it in a protective case. Regular calibration against known standards helps maintain accuracy. Typical precision is about 0.01–0.02 mm for well-made vernier or digital calipers, with tolerances depending on build quality and method of use.