SMA40WGUU NB Double Wide Block Type:Slide Unit Made in Japan:NB Linear Systems Nippon Bearing Linear Systems SMA40WGUU NB Double Wide Block Slide Unit, The inner diameter is 40mm, Bearing is seals on both sides, The retainer material is resin, Bearing is a high accuracy grade linear bushings, Series mainly used in the USA, NB brand (Nippon Bearing Linear Systems), made in Japan.