1 or 2 Shimano XTR SM-RT99-XT SM-RT81 Center Lock Disc Brake Lock Ring W/Washer | eBay
Amazon.com: Pwshymi Bike Brake Rotors, Disc Center Cover Bike Centerlock Lock Lockring Ring Cover Disc Brake Hub Rotor Lockring 9/12/15mm Black for Road Bike Mountain Bike Sram Centerlock Ring Nut(One set) :