ABI Enduro XD-15 External GXP Bottom Bracket: 100% USA made with aircraft grade metals. Grade 3 CEREBEC USA Silicon Nitride ceramic 3/16 balls. Angular Contact design bottom bracket allows fine tuning of preload. Nitrogen nickel stainless steel races are lighter, smoother and more durable than any other available on the market. Will not rust, and lasts 5 times longer than any other ceramic bearing. Mountain BB cups will fit 68/73mm shells.