Direct Calibration Chain for Hand Torque Screwdrivers from the National Torque Standard

Hand torque screwdrivers are used for the fastening control of screws in almost all precise mechanical and electrical parts. This paper describes the realization of a direct calibration chain for hand torque screwdrivers traceable to the national torque standard. The calibration methods for a reference torque screwdriver using a primary torque standard machine, a torque screwdriver tester using the reference torque screwdriver, and hand torque screwdrivers using the torque screwdriver tester are described respectively. Uncertainty evaluation methods for each calibration level are also explained. The effectiveness of the calibration chain for hand torque screwdrivers could be demonstrated.