This is the Vented Steel Brake Disc from Ultimate Racing. It is machined from black anodized steel. Intended for Mugen and Sworkz among others.
Thanks to the holes and slots we get a lower temperature which results in less wear and a more uniform braking feel.
Due to these grooves, we also achieve significant weight savings. The Ultimate brake discs are 30% lighter than the original Mugen discs. This weight savings in rotational mass translates into faster acceleration and lower fuel consumption.