The Wolf Tooth MK0 BSA Bottom Bracket brings ceramic speed to a design built to survive real riding, not just a lab test. Custom race-sealed ceramic bearings spin with low drag while resisting the water, mud, and grit that usually wreck softer bearing seals. Polymer spindle bushings separate the bearing race from the crank spindle, cutting out the metal-on-metal contact that causes bottom brackets to creak. An adjustable-width shell handles 68 to 73mm BSA shells in one part, with 83mm DH and 100mm fat bike sleeves available separately for wider builds. What Our Gearhead(R) Experts Are Saying:"I ran a set of these through a full mud season without a single bearing service, and they still spin as smooth as the day I installed them. The sealing does what most ceramic bottom brackets promise and don't deliver."