Skidmore-Wilhelm Bolt Tension Calibrators are designed for testing a wide variety of fasteners and for calibrating impact wrenches. Each calibrator is essentially a hydraulic load cell with a hole in the center for inserting a sample bolt, nut and washer. As the bolt and nut are tightened, they compress the load cell, creating an internal pressure. A gage measures the pressure and provides a dial readout calibrated in pounds-tension equivalent to the tension created in the fastener.