ABEC-5 Ball Bearing 15x28x7 Stainless Steel Ceramic Balls (Si3N4 Silicon Nitride) A high quality ball bearing Stainless Steel Ceramic Balls ABEC-5 quality, this is a popular size that could be used in many application that uses this size 15x 28x 7Bearings can rotate up to 100,000 rpm, each bearing has 2 Rubber Seals to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease.