Not all brake rotors are created equal. These rotors are cast to very high material specification and tight tolerances. The slots extend brake pad life by "wiping" the white-hot boundary layer from the disc and pad, increasing braking efficiency and extending pad life, and they have ramped edges to cut down on noise.
The rotors have a zinc plating to keep the rotors from rusting outside of the pad contact area. This is friendlier for pads than cadmium. Factory size, these are a direct replacement for stock parts. Sold in pairs. Fits 2001-02 US cars with the Sport Package brakes and all 2003-05 US Miatas and Mazdaspeeds.
The brake size varied on Miatas sold outside the US after 2002. These are 10.9" in diameter, please check your brakes before ordering if you're not sure.