The Shimano RT-6B750 is a 6-bolt disc brake rotor built from 2. 2mm stainless steel for improved strength, heat capacity, and resistance to trail debris over standard 1. 75mm rotors. Riders asked, and Shimano delivered. What Our Gearhead(R) Experts Are Saying:"The extra thickness makes a noticeable difference on long descents where thinner rotors start to fade. The 2. 2mm construction also handles hits that can take a standard rotor out of service mid-ride."