These are the same high quality industrial bearings that come as original equipment on any of Whiteside's bearing mounted router bits. Replace worn out bearings, interchange with existing bearings to automatically change cutting depths, or add them to bit shanks to make bits bearing guided. Be sure to add the appropriate size lock collar (either #RLC14 or #RLC12) when adding bearings to bit shanks. #R3S and #RBB300 bearings have no-mar nylon sleeves. RBT3 bearings have Teflon shields. Bearing #RB3U & RB9U are undersized for re-sharps. OD = Outer Diameter. ID - Inner Diameter. Made by Whiteside. USA