Having the right items in your Save-a-Dive Kit can make the difference between a great dive and no dive, thanks to equipment malfunction. Don't be left behind on the beach or the boat because of a bad Valve-to-Cylinder O-Ring. O-Make sure to include Spare Tank Neck O-Rings in your Save-A-Dive kit! O-Ring is a Universal Valve-to-Cylinder O-Ring for 3/4" Threaded Cylinders and is made of Durable Buna-N Rubber. O-Ring is designed for Air Use.