Advantages of the calibration chain for hand torque screwdrivers traceable to the national torque standard

Hand torque screwdrivers (HTDs) are ordinarily calibrated (or verified) by using torque screwdriver testers (TDTs). Weights, bars, wires and pulley devices (called Weights and Bar System: WBS) have been conventionally used for the calibration of the TDTs as reference standards, where the mass of weights and the length of bars are separately calibrated by using each reference standard of much higher grade. However, the consistency of torque realized by the weights and bars with the torque traceable to the national torque standard has been unclear. The authors tried to establish a calibration chain for HTD traceable to the national standard of torque, utilizing a reference torque screwdriver (RTD), which is directly calibrated by the torque standard machine at NMIJ / AIST. The authors also compared TDT calibration results using RTD and WBS.