10 Ball Bearings 6904ZZ 20 x 37 x 9 mm Set of 10 Ball Bearings 6904-ZZ, the inner diameter is 20, outer diameter is 37 and the width is 9, this is a popular size that could be used in many applications, Bearings are made of Chrome Steel and can rotate up to 19000 rpm, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease, Bearings are packed 10 bearings in one plastic tube.