The bolts always work together with a nut. A nut fastener is a mechanical fastener with a threaded hole. It is attached to a bolt, screw or stud to provide a clamping force and prevent axial movement. For example, a bolt is inserted through two parts, with aligned holes, and a nut is then screwed onto the bolt. The shaft of the bolt prevents radial movement of the parts, while the head of the bolt and the nut together prevent axial movement. http://www.yuchaobolt.com/nut-fastener/