This is the Aerodynamic Steel Brake Disc from Ultimate Racing. It is mechanically processed from black anodized steel. It is intended for Mugen and Sworkz, among others.

Thanks to the holes and slots, lower temperatures are achieved, resulting in reduced wear and a more uniform braking feel.

Due to these grooves, significant weight savings are also achieved. Ultimate brake discs are 30% lighter than the original Mugen brake discs. This weight saving in torque translates to quicker acceleration and lower fuel consumption.