This kind of bearing is suitable for the parts in which the radial size is specially limited. Since the bearing has not collar, the surface of shaft journal and the surface of housing inner bore are directly acted as rolling face. It is requested that the hardness, surface roughness and size accuracy of shaft journal surface and housing inner bore surface fitted with it be adaptable to the collar of bearing. Another pivot cylinder is modified as flat cylinder with M-type cage structure. Its speed performance is greatly improved