Ball Bearings 30x42x7 Chrome Steel With Snap Ring (C clip) 6806ZZNR Ball Bearings with Snap Ring (C clip), this is a popular size that could be used in any application that uses this size 30mm x 42mm x 7mm. Bearings are made of Chrome Steel and can rotate up to 15,000 rpm, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease