Full Ceramic Bearing Silicon Nitride 13x25x6mm13 x 25 x 6 Full Ceramic Bearing Si3N4 Silicon Nitride 13mm x 25mm x 6mm This full ceramic bearing features both races and balls made from silicon nitride (Si3N4), offering high speed, non magnetic, and corrosion resistant performance. With a 13mm inner diameter, it's often used in RC engines like the Nova Rossi 16011 and other high RPM setups where metal just cant keep up. Full ceramic build with Si3N4 races and balls PTFE cage for low friction