ACB 3645 CC SXD - 1-1/8" Angular Contact Bearing (30.2 mm x 41 mm x 6.5 mm: 36x45 degrees), internal headset bearing with XD15 balls and bushings for lifetime corrosion resistance. This is the last headset bearing you will install in your bike. These XD15 bearings are virtually identical in performance and corrosion resistance to our XD15 ceramic hybrid bearings used in hubs and bottom brackets, but with XD15 balls that perform better in the harsher steering environment. The mechanical properties of the XD15 stainless steel balls provide a higher level of shock resistance than ceramic balls for headset applications. The Enduro-tested bearings with XD15 balls and bushings have been used for months in saltwater without any corrosion; there is simply nothing comparable on the market. This bearing size is also known in the bicycle industry under the following part numbers: 27287-1046-004, HSS 20130K, TH-873E, MR-122. The Enduro line of angular contact bearings for headsets starts with rings made of black oxidized chrome steel, progresses to 440C stainless steel, and the top product is XD15 stainless steel for aerospace (rings and balls) with a lifetime warranty. They are always constructed with the largest possible balls, feature double-lip seals sitting in a micro groove (labyrinth), and are filled 90% with waterproof high-pressure grease to provide ultimate protection against sweat and the elements. The Enduro angular contact bearings (A/C) are designed so that all balls engage evenly to distribute the load over a larger area, minimizing wear and maximizing lifespan.