This is a replacement ProTek R/C 7x19x6mm Front Bearing. This bearing is designed to fit the ProTek R/C Samurai 321B, RM, S03 and R03 Nitro Engine, but is also compatible with most O.S. .21 engines. This bearing will also fit any other .21 competition buggy engine that uses the same bearing dimensions; 7mm inner diameter, 19mm outer diameter and 6mm thick. This bearing is shielded only on the outside; the inside is open to allow the ball proper lubrication.