SHIMANO GRX / ULTEGRA RT-CL800 Center Lock Disc Brake Rotor

Quieter than ever, but with superb, consistent braking performance on any long, steep descents thanks to excellent heat dissipation
The new arm shape is more robust, leading to quieter operation

Heat dissipation paint boosts performance

External lockrings are mostly needed on 15mm axle bikes
Internal lockrings are for 12mm thru axles.