CNC machined from 6061 T6511 aluminum. Machined surfaces allow for better caliper alignment and a more rigid brake setup. The Post Mount standard is universal to the front and rear brakes. Some frames/forks use a 160mm rotor with no adapter, some use a 180mm with no adapter. Check your frame/fork! Our adapters can be used on both forks and frames with 160mm and 180mm posts. Bumping up from a 203mm post mount (2015-2020 Fox 40 and 49 forks) to a 220 or 223mm rotor is also covered by our adapters. Picking the Correct Adapter To go from a 160mm post mount to a 203mm rotor, you need a 43mm adapter. To go from a 160mm post mount to a 200mm rotor, you need a 40mm adapter. To go from a 160mm post mount to a 180mm rotor, you need a 20mm adapter and so on. For 2016+ Fox 36 and 180mm rear brake mounts: You will need the 23mm adapter to work with the 180mm post mount and a 203mm rotor. Going from a 180mm post mount to a 200mm rotor requires the regular 20mm adapter.