Upgrade you stock bottom bracket. Enduro bottom brackets are designed to spin more efficiently and for longer. Proven time and again in World Cup race conditions, the ZERO Ceramic bearings are the ultimate race day weapon. Oversized Grade 3 balls roll on races which are ground to a mirror finish after receiving Magnetite and then Cryogenic treatments for hardness and longevity. More durable and with even lower rolling resistance than any 2RS bearings, they come closer to that magic ?zero rolling resistance number. Enduro Bearings uses Silicone seals which are more slippery than rubber seals used by other ceramic bearing suppliers.Fits BB90 frames - 37mm diameter with a shell width 90.5mm (road) or 95.5mm (mountain)Suitable for chainsets with 24mm axleLightweight, durable Delrin cupsZero Ceramic Bearings42.48g