Ball Bearings 6902 ZZ 15 x 28 x 7 Quality Ball Bearings6902-ZZ, the inner diameter is 15, outer diameter is 28 and the width is 7, this is a popular size that could be used in many applications, Bearings are made of Chrome Steel and can rotate up to 26000 rpm, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease.