The 138190042 M14 Flywheel Nut secures the flywheel to the crankshaft. 

The nut will also hold the starter cup and plastic flywheel fan to the flywheel and crankshaft. If you are having trouble loosening the nut or flywheel, try a penetrating oil such as WD-40 or gently tapping the end of the crankshaft with a plastic hammer. The penetrating lube and hammering helps to knock off the corrosion and metal transferred by harmonics. Do not hit the flywheel, or it may damage it. These M14 Nuts are the OEM Replacement for 196cc 6.5hp Clone, Honda GX200, Ducar 196, Ducar/Tillotson 212, Tillotson 196R/RS, Tillotson 212R, Tillotson 225RS, and BSP 196 and 212 Engines. 

Thread Dia M14-1.5

Torque Spec: 55ft/lbs