SW64-OP Bore linear motion ball bushings/bearings, the inner diameter(bore) is 4 inch dimensions with steel retainer, bearing is a high accuracy grade linear bushings, series mainly used in the USA, NB brand (Nippon Bearing Linear Systems), made in Japan. Type: NB Linear Systems Ball Bushing. Number of Ball Circuits: 5. SW64-OP:Made in Japan:NB Linear Systems Nippon Bearing Linear Systems SW64-OP Bore linear motion ball bushings/bearings, the inner diameter(bore) is 4 inch dimensions with steel retainer, bearing is a high accuracy grade linear bushings, series mainly used in the USA, NB brand (Nippon Bearing Linear Systems), made in Japan.