1. Suitable for hollow steel, and wood doors with any kinds of frame, reversible hand installation. 2. Adjusting spring power, from size 2 to size 4 Multi size3. According to installed dimension be able to select desirable opening angle4. Universal application for STANDARD, TOP JAMB and PARALLEL arm installation.5. Precise two speed adjusting valve for control door closing smoothly.6. Standard adjustable BACK CHECK