These pulleys spin on Grade 3, Abec 5 Kogel Ceramic bearings. The same bearings as our bottom brackets. Choose road bearings for lowest friction on road bikes or cross bearings if durability is key (that's for you, cross and gravel racers). The wheels are made of aluminum, which will make them more resistant to wear in muddy conditions. Out of the box, these pulleys will fit on: Shimano road and MTB 10 and 11 speed Campagnolo 11 speed Sram 2x MTB 10speed Sram 10 and 11 speed road groups Important Fitment Notes** For Sram road groups, the bore of the top pulley is different, please choose this from the dropdown menu. For Sram 1x derailleurs, please look at our 12 tooth Narrow Wide Pulleys Not compatible with Campagnolo 10 speed Looking for our "Not for Instagram" pulleys you have seen spinning -almost- for eternity, they are right here .