Material: This ball bearing holder is made of high-quality, durable, and high-strength steel. Package Contents: 4 x 6mm x 9 ball bicycle crank bearings. One pair of crank bearings for replacement, one pair for spares. Bearing Size: Outer diameter: 29mm, inner diameter: 18.4mm, ball size: 6mm x 9 balls. Please check the size before purchasing! Multiple Uses: This ball bearing holder is for replacing bicycle parts and is suitable for regular bicycles, mountain bikes, mongoose bikes, lowrider bikes, stretch bikes, and children's bikes. Note: If you receive a 6-ball bearing holder, it is the same product, size, and use. This does not affect its functionality. Because they update the iterative relationships. Numerous uses: This ball bearing support for bicycle parts replacement is suitable for bicycle cranks, such as those found on: mountain bikes, children's bikes, lowrider bikes, kids' bikes, and extendable bikes.