Threading is the process of creating a screw thread. This is a defining factor for the shape of a screw thread. Undercut studs have a shank equal to the pitch diameter of the screw thread. The nine lugs are actually sections of a screw thread. Also, pitch diameter may refer to that dimension of a screw thread. Typically the finial is externally decorative whilst hiding an internal screw thread. Trapezoidal thread forms are screw thread profiles with trapezoidal outlines. A more recent approach uses a screw thread. It establishes the criteria for screw thread acceptance when a gauging system is used. The lead for a screw thread is the axial travel for a single revolution. Originally, the mounting holes were tapped with a particular screw thread. It also establishes the criteria for screw thread acceptance when a gauging system is used. The center of the bit is a tapered screw thread. Other semi-standard screw thread sizes are available for certain specific applications. Standard screw thread sizes allowed interchangeable parts and the development of mass production.