TK20 Self Aligning Ball Bushings 20mm Linear MotionTK20: TopBall High Load Standard Linear Systems Self Aligning Ball Bushing TK20 20 Bore High Load Standard type TopBall metric type linear motion ball bushings bearing inner diameter(bore) is 20 mm 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