Shimano RT56 Disc Brake Rotor The Shimano SM-RT56 6-bolt brake rotor consists of one-piece moulded stainless steel, which has also been heat-treated and polished. It is available in 160 mm and 180 mm diameter and can be used for XTR, XT, SLX, Deore and many other MTB and City & Touring brakes. Note that SM-RT56 is only compatible with organic brake pads.