This taper was designed by Bridgeport Machines, Inc. for use in its milling machines. R8 tapers are not self-holding, so they require a drawbar extending up through the spindle to the top of the machine to prevent loosening when lateral forces are encountered. They are also keyed (see image) to prevent rotation during insertion and removal, although it is the taper that transmits torque in use. The drawbar thread is typically ″–20 tpi (UNF). The angle of the cone is 16°51′ (16.85°) with an OD of 1.25″ and a length of ″. (source, Bridgeport Manufacturer) The diameter of the parallel locating portion is not a "fractional inch" size like the other dimensions and is 0.949″ to 0.9495″.