Fit Perfectly - ISO 492:2005 Standard, the aperture tolerance range is controlled between 7um, ensuring a great fit. Roll Smoothly - Internal G5 steel ball and synthetic grease minimize friction, improving rotation efficiency. Without Backlash - Under non-load conditions, the radial swing play is within the 9um range. Dimensions Correspond - Inner ID 15mm, Outer OD 26mm, Width B 7mm, matching the rear hubs of the bike. Specialized recommends replacing these about once every 6 months with aggressive riding and once a year for passive riding. The aperture tolerance range is controlled between 7um, ensuring a great fit. Internal G5 steel ball and synthetic grease minimize friction, improving rotation efficiency. Under non-load conditions, the radial swing play is within the 9um range. Inner ID 15mm, Outer OD 26mm, Width B 7mm, matching the rear hubs of the bike. Specialized recommends replacing these about once every 6 months with aggressive riding and once a year for passive riding. Color: Silver Material: Stainless Steel Package Contents: 1xBall Bearing Kit Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.