Micrometer screw gauge. This is an instrument used to accurately measure small distances. Here it is being used to measure the thickness of a piece of wire (upper left). The wire is seen end on, and is held by the adjustable measuring clamp, which has been tightened (screw handle at right) until the wire is loosely clamped. The measured value is obtained using two gauges. The first (not clearly seen) measures to an accuracy of 0.5 millimetres. The circular gauge (seen here) provides further accuracy to 0.01 millimetres. The wire is shown to be 0.47 millimetres thick. This micrometer has a maximum measuring capacity of 25 millimetres.