This is a Novarossi ceramic rear engine bearing for the Novarossi P5X, 528X and RB Concepts TM928 off-road competition buggy and truck engines. This bearing also fits recent Novarossi and RB Concepts engines that require the special 25.8 mm rear bearings. The bearing dimensions are 14mm I.D., 25.8mm O.D., and 6mm thick. This bearing is open to allow oil to lubricate the bearings during use. This bearing will also fit any other .21 to .28 competition engine that uses the same bearing dimensions. Install the bearing with the opening towards the rear of the engine.