1. Suitable for hollow steel and wood door with any kind of frame, reversible hand installation 2. Adjustable spring power designed, provide two of power range version, from size 1 to size 4 and from size 2 to size 5 stepless regulation, less inventory for wider user needs. 3. According to different installation dimension be able to select desirable opening angle 4. Universal application for standard, top jamb or parallel arm installation 5. Precise two speed adjusting valve for control door closing smoothly 6. DELAY ACTION, BACK CHECK, Both can be adjust in filed for different application