BOX COMPONENTS Extremum Raceprep BMX Bicycle Bottom Bracket - BX-BB13EXRAC The extremum race prep bottom bracket is the first external BB designed for BMX racing Unlike mountain biking where bikes are Exposed mud and water, BMX racers typically ride in relatively clean environments Meets or exceeds enbmx standards Extremum race prep bottom brackets may require more frequent maintenance, depending on your riding habits Available in anodized Red, Blue, Gold and Black to fit all 24-millimeter bottom bracket spindles and 68 or 73 x Bc1.37 inch bottom bracket shells