CNC machined from heat-treated, closed die, steel forging Stronger than cast iron or late style steel flywheels 5-piece design - easily rebuilt with standard flywheel fixtures and tools Unassembled balanced flywheels are balanced by the static method Kit contains Flywheels, pinion shaft and sprocket shaft, connecting rods S&S Cycle flywheels for Sportster models feature removable mainshafts for easy rebuilding. In addition, the S&S Cycle pinion shaft is the 1986-87 splined design, which is much stronger than the stock pinion shaft, allowing the use of higher lift cams and stronger valve springs. Designed for 1200cc Sportsters (stock displacement), 3-13/16" stroke (stock), 7-7/8" flywheel diameter (stock)