Brake Adapters can be used to attach Shimano postmount brake calipers to frames or forks with postmount mounts.
ADP-31: For post-mount brake caliper to post-mount adapter / 180 mm disc / for Shimano older than 2012
ADP-32: For post-mount brake caliper mounting on the fork on post-mount support / 180 mm disc / for Shimano after 2013