[Material]: The ball bearing retainer is made of steel, which is of good quality, durable and high strength. [Size]: Outer diameter: 29mm/1.14inch, Inner diameter: 19 mm/0.75inch, one package includes: 4 bicycle ball bearings, you can use one pair, leave the other pair for spare [Product features]: The retainer is inlaid with 9 stainless steel balls, which are firm and do not fall off, and the balls are lubricated and rotate well. [Use]: Suitable for replacing bicycle crank bearings, suitable for the bottom bracket bearings of ordinary bicycles mountain bikes [Precautions]: Before purchasing, please confirm whether the size of your bicycle accessories matches this bearing.