Mechanical torque wrench is the most common type of torque wrench. The torque value is set by turning the handle, and the operator can read it on the torque wrench body or on a small sliding dial clock. After mounting the socket on the square drive, the torque wrench is employed as a common tool for sockets. The achievement of the set torque is marked by a release. After setting the torque value, it is usually possible to lock the handle or the spindle to prevent accidental changes. The control mechanism is included in the instrument and it is essentially constituted by a strong spring, whose preload, by means of the knob or of the control rod, determines the torque value. The square drive where is grafted the socket is prevented in the rotation by a tooth, kept in position by a ball which stands on the springhead.