18307 Ceramic Ball Bearing from World Champions ACER Racing. This is a 18x30x7mm ceramic ball bearing with an 18mm inner diameter x 30mm outer diameter and 7mm width. Uses diamond polished Silicon Nitride Ceramic Balls. Price is for one 6903 ball bearing so please choose the quantity you wish to order. 

The advantages of our ceramic bearings are vast including lighter weight, lower friction and heat, greater speeds and much greater durability especially for competitive cycling use. Fully sealed on both sides. We are the industry leader since 1989.