Flat mount disc brakes bring the caliper closer to the frame or fork. While most front Flat Mount calipers include the proper adapter plate and hardware to give you the option of 140 or 160mm rotor use, if you are switching bikes or simply need an adapter, SRAM offers this stainless steel mount and hardware to get you set-up. This is considered a 0mm/20mm mount, as most forks are designed for the 140mm set-up, so you run it to the zero side, and if you plan to run a 160mm, you mount it to the 20mm side.