SWT4UU NB:Made in Japan:NB Linear Systems Two Side Cut Flange Type Nippon Bearing Linear Systems SWT4UU NB 0.25" Bore linear motion ball bushings/bearings, the inner diameter(bore) is 0.25" inch dimensions with steel retainer, bearing is a high accuracy grade linear bushings, series mainly used in the USA, NB brand (Nippon Bearing Linear Systems), made in Japan.