Collet
A precision clamping device that grips a cylindrical workpiece or tool shank by contracting around it when a nut is tightened. Collets provide high clamping force and concentricity (runout < 0.01mm). They are used in robot tool changers, CNC machining, and precision assembly to mount end-effectors, sensors, or tools on robot wrists.
See this in practice: the hardware store →
Hardware