A bottom bracket on a bicycle connects the crankset to the bike and allows the crankset to rotate freely. The bottom bracket contains a spindle which the crankset attaches to. Bearings allow the spindle and cranks to rotate. The chain rings and pedals attach to the crank shaft. Bottom brackets come in sealed or unsealed options. Dan's Comp carries a large selection of complete bottom bracket kits and bottom bracket accessories such as replacement bolts, spindles and spacers.