Enduro says that races are won and lost by derailleur pulley drag. Enduro Zero Pulley Assemblies use grade 5 ceramic bearings. Enduro’s ceramic bearings use ABEC 5 precision cartridge bearings and CERBEC USA Grade 3 Si3n4 Silicon Nitride balls. The races receive 3 cryogenic treatments and a rust proof Magnetite finish. Sold as a pair. Compatible with 9- and 10-speed systems.