High durability to withstand repeated opening and closing of the door. The screws at the end of the pneumatic door closer make it easy to increase or decrease the closing speed and force of the door, making it easier for people to get in and out and at the same time prolonging the life of the door and the frame. Full 90 degree opening. It is recommended that individual closers be used for light to medium weight doors and pairs of closers (one above the door and one below the door) be used for heavier storm and screen doors. Includes all mounting hardware, no need to order or add additional parts, easy to install ,please refer to the manual (on the package) for detailed installation procedures! CASONNIK Door Closer,White,Standard Duty Pneumatic Screen and Storm Door Closer