Bearings ACB S8551 BO - ABEC 5

The Enduro Bearings ACB S8551 BO is an angular-contact headset bearing built with 45 x 45 degree contact angles for 1-3/8 inch headsets. Races are made from Black Oxide/Magnetite treated 52100 high-carbon chromium alloy, rated ABEC 5 with Grade 10 balls. This bearing also serves as the Future Shock headset bearing on Specialized Roubaix, Ruby and Diverge frames from 2017 onward.

Each race receives a secondary super grind polish for a smooth rolling surface, then a multi-bath Black Oxide treatment that adds roughly 3 microns of anti-corrosive depth and extra toughness. Dual-lip LLB seals ride in a labyrinth groove, and the cavity is filled 90% with Almagard 3752 grease. Static load rating is 660 lbf (2.93 kN); claimed weight is 20.05 grams.

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