Shoulder screws or shoulder bolts are versatile little items that can be used as a fastener for links and pulleys or can attach gears to machinery. The shoulder screw is unique in that it is made up of three parts: the head, the shoulder and the thread. Shoulder screws specifications are given by shoulder diameter first and the shoulder length. Be sure to choose the right one for your application. When choosing hex-head shoulder screws be sure you have hex keys on hand for tightening.