BMX Hollow Tech II crankset for serious racing using the new external bottom bracket bearing system to maximum effect Lightweight yet rigid design is highly durable & incredibly strong Hollow Tech II bottom brackets bearings are mounted outboard of the frame increasing there diameter & placing them more widely apart; this dramatically changes the load on the bearings increasing rigidity & bearing service life We recommend that this bottom bracket is initially installed by a bike shop to ensure perfect bottom bracket facing & fit Comes complete with chain ring fixing bolts & nuts For use with a single chainring in a choice of sizes from 34 tooth to 46 tooth