A screw is a conical fastener consisting of a protruding helix around a central shaft that acts as a wedge as it pushes into the fastened material. They are identified by head types such as cheese, flat, hex, knob, truss and pan. Bolts are cylindrical, threaded fasteners for the assembly of non-threaded components with the aid of a nut. They are identified by head types such as binding, cheese, flat, hex, oval, pan, round, spade and truss.