The big nut (hold the jokes) used on the 568/543/523 and 89 555/520 input shaft to retain 5th gear. Does anyone know the thread pitch/size ? I believe its metric like an M20 but I dont know and dont have one here handy to check it out. Not available from mopar anymore so I was gonna see if someone like Mcmaster sells a high strength locknut equivelent and get a quantity to sell along with the snap rings.