These inserts are installed in PFC calipers to protect the aluminum threads from stripping. The M10x1.0 male threads fit all PFC calipers. Female 1/4-28 threads accept a 1/4-28 Bleeder Screws (Part No. PF900-900104-01) or 1/4-28 Speed Bleeders (Part No. 3266-16). Bleed screws sold separately. Set of 2 inserts, enough for one caliper.