Torque or moment of force is the tendency of a force to rotate an object about an axis or fulcrum. In mathematics, torque is defined as a distance and force vector, which tends to produce rotation. Loosely speaking, torque is a measure of the turning force on an object such as a bolt or a flywheel. Usually the symbol for torque is the Greek letter Tau (T); sometimes it can be denoted by the letter «M» from the word «moment». The SI unit for torque is the Newton meter (N•m). The units: pound-force-foot, pound-force-inch and ounce-force-foot are also used for torque. For all these quantities the word «force» is often left out, for example, pound-force-inch is abbreviated to «foot-inch».