SparkFun ROB-12509 Swivel Hub
The swivel hub lets you connect any two parts with the 0.77" hub pattern together and have them swivel a full 360 degrees. Internal ball bearings allow for smooth motion. Tapped 6-32 holes are on both sides, making attachment easy. Use these wherever you need a smooth swivel motion such as a wheel mount or rotating platter.
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.