The S&S crankpin nut clearancing gauges are designed to simplify and eliminate clearancing problems that may arise when installing stroker flywheels in stock big twin crankcases. By painting the bosses to be clearanced and then placing the appropriate gauge on the main bearing race, the crankcases can be marked with a scribe in the proper location for the stroke and style connecting rod crankpin nuts to be used, quickly, and precisely. Fits 1958-1999 Harley-Davidson big twin engines. S&S Part #: 53-0005