These linkages use 6-32 screw rod (not included) to create custom arms for just about any application. They have a 0.25" free-moving ball (with a 0.14" diameter bore) in the end for smooth movement and easy connectivity. They are sold in packs of 12 and come with cup washers as well.
Actobotics is a robotics building system based around extruded aluminum channels, gears, precision shafts, and ball bearings. Thanks to the two standardized hole patterns, nearly all Actobotics components can be intuitively connected together. The wide range of components makes building complex electromechanical prototypes or finished projects a reality.