SW4UU Seals on both sides NB Nippon Bearing Linear Systems Made in Japan SW4UU 1/4" Bore linear motion ball bushings/bearings, SW4UU is Seals on both sides, inner diameter(bore) is 1/4" 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.