StopTech Replacement 42mm Dust Boot for ST-22/ST-40/ST-45/ST-60/ST-65 StopTech offers Rebuild Parts for Calipers, Big Brake Kits and more. Overhaul your kit today to keep them in tip-top shape. *Caliper Rebuild Kits* Include components to rebuild ONE pair of piston bores. For ST-22 calipers, only one kit is required. For ST-40 and ST-45 calipers, two kits are required (one kit for each piston size). For ST-60 and ST-65 calipers, three kits are required (one kit for each piston size).