[Material]: The ball bearing retainer is made of steel, which is of good quality, durable and high strength. [Size] : Outer Diameter: 20.5 mm / 0.8"; Inner diameter: 13 mm / 0.5",BALL DIAMETER: 3/16 inch.One package includes: 4 bicycle ball bearings [Product features]: The retainer is inlaid with 7 stainless steel balls, which are firm and do not fall off, and the balls are lubricated and rotated. [Use]: Suitable for replacing the Front wheel bearing of bicycles, suitable for mountain bikes, and Front wheel bearing for ordinary bicycles [Precautions]: Before purchasing, please confirm whether the size of your bicycle accessories matches this bearing.