TK40 NB TopBall Linear Systems Bearing 40mm Inner Diameter Made in Japan TK40 NB 40mm Bore Standard TopBall type linear motion ball bushings bearings, inner diameter(bore) is 25mm dimensions with built-in seals, the Topball slide bush is a high performance bushing with three times the load capacity, capable of providing up to 27 times normal travel life of a conventional slide bushing, high accuracy grade linear bushings, series mainly used in the USA, NB brand (Nippon Bearing Linear Systems), made in Japan.