Keeping your cylinder protected from the elements when it is not connected to a regulator is important to your safety and the reliability of your life support system. Protect your cylinder DIN valve from water, dirt, dust and crawling critters. This non-corrosive Plastic DIN Protector Plug is the kind to ensure proper protection. It slips over the top of your valve to protect your cylinder valve from having water enter inside the delicate internal mechanism when on the deck of the boat or when washing your gear after diving. Cap comes with a loop of line to attach to valve, so its right there when you need it.