The 12-tooth narrow-wide design on these CeramicSpeed pulleys decreases chain articulation and ensures a crisp chain engagement on to and off of each pulley. The symetrical 12-tooth narrow-wide design allows the chain to move smoothly on and off the pulleys without additional friction. CeramicSpeed Pulley Wheels for Shimano 11s, 12-tooth is developed, designed and handbuilt in Denmark and comes with seperate dust covers to fit 9100, R8000, RX, GRX, XT and XTR series derailleurs. In the box:-Two 12-tooth pulley wheels-Alloy Spacer Kit-CeramicSpeed Bearing Oil, 15ml. bottle-Sticker Sheet