Doors up to 40 kg - a pair of door closers (up to 20 kg - 1 door closer). A door closer should be installed in the middle of the door (if only one door closer is installed); the door and the door frame should be kept on a horizontal plane and the drop should not exceed 3 mm. Adjustable tension - To adjust the closing force - Turn clockwise or counterclockwise with a hex key. If you want to use this product, you must have a door frame, and the width of the door frame must be more than 3 cm. Installation is simple and all necessary accessories are included. Comes with 2 door closers and hex keys and screws. Suitable for different types of doors 2 Piece Automatic Door Closer, Silent Spring Door Closer, Adjustable Tension, Max Weight 40kg, Comes with Hex Wrench and Screws It is spring loaded, tension adjustable and can be used for left or right door openings weighing up to 40 kg. Important reminder: 1.. Adjustable Tension - To adjust the closing force - Insert the hex wrench and turn clockwise or counterclockwise. 2. A door closer should be installed in the middle of the door (if only one door closer is installed) 3. The door and door frame should be kept on a horizontal plane and the drop should not exceed 3mm. 4. To use this product, there must be a door frame, and the width of the door frame must be greater than 3 cm. 5. If it is a heavy door (weight 40 kg), two door closers should be installed, and the best installation position is the upper and lower position, so that the door can be closed normally.