A caliper gauge is a measuring tool that determines the width or length of an item by fitting it between two arms or prongs on the device. At least one of the arms moves to permit adjustment of the gap until it fits the measured item exactly. Variations of this tool include dial, vernier, and thickness caliper gauges.
The typical structure of a caliper gauge is an "L" shape with one of the caliper arms fixed in position as the shorter leg of the "L." The other caliper arm slides back and forth along the long side of the "L" to allow precise fitting of the calipers around the item being measured. The incremental distances are marked on the long side of the "L" in a standard gauge, beginning with zero where the two calipers meet when the gap is closed. Gauges can also be fitted with an attached digital or dial readout to display the results.
The tips on a caliper gauge can have different shapes. The tips can come to a conical point for an exact measurement at the ends. Pointed tips can have flat interior sides to fit snugly against an item's surface. Caliper tips can bend inward 90 degrees to accommodate a grooved or threaded surface.
A dial caliper gauge is specifically intended for internal cylinder or pipe measurement. Two bent prongs are inserted into the cylinder and spread using a spring-loaded adjustment until the points touch the insides of the cylinder. The dial display has a bezel which is zeroed before measurement to ensure accuracy. Some "L" shape caliper gauges are also fitted with bent prongs on the opposite side from the regular calipers to measure an internal diameter.
Vernier caliper gauges add an extra measuring gradient to the standard "L" shape gauge. A vernier scale uses a measure of 90% of the standard scale on the gauge to provide an exact reading for one additional decimal place. It is used when precision is essential.
Sometimes it is necessary to measure the thickness of a length of fabric or a belt on processing equipment. A modification of a caliper gauge called a thickness gauge can be used for this purpose. From a handle on one end, two arms extend to the side with flat or rounded spring-loaded tips pointing toward each other at 90 degree angles from the arms. The arms are slipped over either side of a belt or piece of fabric, and the gauge reads the thickness as the fabric or belt passes between the arms.