Designed to fit onto the butt hinge pins，quick and easy fix to keep the door closed Sturdy contrucion, Chrome finish. Inside diameter: 18mm; Outside diamteter: 25mm. Easy to install: 1.close the door, pull up the hinging bolt about 25mm; 2.spread the arms of the closer open with some strength and slide it over the portion of the hinge pin; 3.slowly allow the arms of the closer to rest against the door and the frame Tips: 1.oil before using to stop squeaking; 2.put a small piece of cardboard or cotton layer in between the closer and door to avoid paint peeling or wear due to friction Package: 4 x hinge door closer. You can freely choose the number of installations, Manufacturer: Young Wolf