SWK4GUU NB:Made in Japan:NB Linear Systems Square Flange Type Nippon Bearing Linear Systems SWK4GUU NB 1/4" Bore linear motion ball bushings/bearings, the inner diameter(bore) is 1/4" inch dimensions with resin retainer, bearing has seals on both sides, bearing is a high accuracy grade linear bushings, series mainly used in the USA, NB brand (Nippon Bearing Linear Systems), made in Japan.