Making a great bearing starts with having the a lot of expertise and using the best materials. Bullseye uses super hard Chrome Steel balls that measure 65 on the Rockwell Scale; each ball is tested to ensure that is perfectly round. The balls run in deep-grove race ways and are retained by a self-lubricating Delrin crown. A low viscosity synthetic oil bas been added to make these bearings spin great while keeping friction levels at a minimum. Each bearing feature dual rubber shields(seals) to protect the bearing from dust and other contaminates. The shields also make this bearing completely serviceable.