Shimano Ceramic Bearing for Line Rollers, Set of 2, Ceramic Bearings TYPE-S Line Roller is a type of bearing that combines durability, smoothness and ultra-microscope. Can be used in fresh water without oiling (not absolutely rust). Reduces line problems to the extremes. Even if the oil is used, it can reduce line problems with low viscosity oil. In addition, the salt requires oil, but the oil viscosity is lower than stainless steel bearings, reducing line issues.