Mounting screws for Sram Flat Mount brake calipers on frames or forks. The different lengths are required for the varying thicknesses of the rear stays. The screws must completely pass through these, plus an additional 10 mm of thread for attaching the brake caliper or adapter. Generally, 15 mm long screws are sufficient for the front. Sram supplies rear brakes with screw lengths of 27 and 32 mm, and front brakes with a length of 15 mm.