Shimano XT SM-RT81 Disc Brake Rotor Centerlock Ring and Washer Description: This Shimano XT SM-RT81 Disc Brake Rotor Centerlock Ring and Washer is intended to affix Centerlock disc brake rotors to Centerlock compatible hubs using an internally splined key pattern for tightening and adjustment. Internally splined rotor lock rings are compatible with cassette locking ring tools; this configuration is also an ideal choice for axles measuring smaller than 12mm in diameter. Features: Genuine replacement Shimano parts Centerlock disc brake rotor locking ring Integrated washer helps to retain torque and prevent seizing Internal Spline configuration compatible with cassette locking ring tools Recommended for use with axles smaller than 12mm in diameter Specifications: Compatibility: Centerlock Disc brake hubs (>12mm axle)