SMA50WGUU NB Block Type:Slide Unit Made in Japan:NB Linear Systems Nippon Bearing Linear Systems SMA50WGUU NB Block Slide Unit, The inner diameter is 50mm, 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.