The Assault RC Revolver Series 7x19x6mm Ceramic Engine Bearing provides the maximum performance and reliability to your racing engine at a competitive price. The bearing contains 9 G3 Si3N4 Ceramic Balls riding on an advanced poly inner cage and Chrome Steel 52100 Rings. It has no seals to allow for proper lubrication from the oil in your fuel. Ceramic engine bearings can boost most RC engines an extra 500 rpm with less drag and the life of the bearing is far greater than a steel bearing. Another benefit to ceramics is the weight difference in the balls allowing for less rotating mass.