The specification of the number of screw holes, center-to-center location of those holes, location of the overall pattern, and threading of the mounting holes of a wiper die. Certain patterns are quite common, such as two 3/8″-16 mounting holes on 1.5″ centers for smaller wiper dies (under 3″ tube diameter) and two 1/2″-13 mounting holes on 2″ centers for larger wiper dies (over 3″ tube diameter).