Having six edges, or having a crosssection in the form of a hexagon. Hex Head may refer to screws, bolts, or wrenches such as Allen keys, Allen screws, or Allen wrenches. A shaft is a rotating machine element, usually circular in cross section, which is used to transmit power from one part to another, or from a machine which produces power to a machine which absorbs power. The various members such as pulleys and gears are mounted on it. Specifications. Material Aluminum. Size 21 in.. Height 0.65 in.. Width 20.9 in.. Length 1 in.