The O-ring gland cleaning tool is designed to clean the O-ring gland area on the cylinder to ensure proper sealing between the O-ring and the valve. For aluminum cylinders only! The tool is an excellent way to remove that corrosive build up commonly found in the gland area. The tool utlizes specially cut sandpaper and a guide. The paper does not harm the cylinder and the guide ensures no contaminates enter the cylinder. The specialized machining ensures no metal is removed from the gland area. Includes 10 sets of sandpaper.