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 Delrin Plastic DIN Protector Plug is the best kind to ensure proper protection. It threads in place and has an O-Ring seal to protect your cylinder valve from having water enter inside the delicate internal mechanism when washing your gear after diving.