SMS30G-OP Stainless Steel Anticorrosion Slide Bush Made in Japan:NB Linear Systems Nippon Bearing Linear Systems 30mm Stainless Steel Anticorrosion Linear Slide Bush, It is open, SMS30G-OP bearing is a high accuracy grade linear bushings, The retainer material is resin, series mainly used in the USA, NB brand (Nippon Bearing Linear Systems), made in Japan.