Shimano SM-RT54-ME Disc Brake Rotor - 180mm Center Lock For Resin Pads Only External Spline Lockring. The Shimano SM-RT54 disc brake rotors provide exceptional stopping power in all riding conditions. Shimanos Center Lock mounting system makes installing and removing rotors quick and easy thanks to the spine mount and lock ring design.For use with resin pads onlyCenter Lock lockring design offers fast and easy installation