SMS20G-OP Stainless Steel Anticorrosion: Miniature Slide Bush Made in Japan:NB Linear Systems Nippon Bearing Miniature Linear Systems SMS20G-OP Stainless Steel Anticorrosion Miniature Linear Slide Bush, It is open, The retainer material is resin, SMS20G-OP bearing is a high accuracy grade Miniature linear bushings, series mainly used in the USA, NB brand (Nippon Bearing Linear Systems), made in Japan.