All simulation and experiment results indicate that the performance of ceramic ball bearings is very good, especially in the low-load and high-speed environment. Size: 18T Structure: ceramic bearing Suitable for 4/5/6MM roller screws Apply to most rear derailleur on the market Color: gold Material: aluminum alloy Size: diameter 72mm Package Contents: 2 x Bicycle Rear Derailleur Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in a little different from the real thing. The measurement allowed error is +/- 1-3 cm.