Uses interchangeable Model-A heads in SAE and Metric sizes. Pre-set at factory to desired value within a +/- 4% tolerance. When preset torque value is achieved, a distinct click is felt and heard, followed by a sudden release into several degrees of free movement. Ideal for applications in which one torque value is used extensively. Compact design makes these tools invaluable in hard to reach locations. Tools automatically reset when torquing- force is removed.Accuracy +/- 4%.