The Super Nut is an original James designed mainshaft nut that has a strong reputation stretching several decades. The added benefit? This mainshaft nut, with built-in replaceable seal, will help you keep the transmission oil where it belongs… Inside. Note: Due to the added height it may interfere with some mainshaft support or inner primary cases. Note: See 518760 for James replacement seal & 517165 for replacement lock tab washer.