[OE NUMBER]90179-18020, 90215-21256[FITMENT]Suitable for Yamaha 660R models from 2001 to 2005. Please verify your vehicle's make, model, year, and OE number before purchasing to ensure compatibility.[FEATURES]Material: Crafted from chromoly steel for enhanced durability and strict tolerances, ensuring precise alignment.Design: Features a 13-tooth bolt washer that is CNC precision-machined to remain durable and resistant to deformation.[INSTALLATION]Step-by-Step Guide: The lock washer has internal splines similar to the shaft. Align these splines properly.Hold the outer edge of the lock washer to ensure it engages with the splines.Place the nut on and tighten it using a torque wrench set to 50 foot-pounds.Finally, fold over the lock washer to secure it firmly in place.[PACKAGE CONTENTS]Includes 1x Front Sprocket Holder Lock Nut and 1x Bolt Washer.For professional installation methods, especially when replacing the flywheel and stator, please refer to the relevant instructional videos.