Spring type with ball chain operation, smooth and free orientation. Specification:Diameter: Φ36Material: AluminiumSpring length: 620mm, 510mm and 400mm. Main Components: controller, coil winder, slowdown machine, spring linker, spring, head rail, headrail bracket, speed regulator, upper tube, circular ball chain, underbeam end stop, underbeam. Features:Circular ball chain type auto spring roller ...