It is expensive and time consuming to have your tank cleaned for use with nitrox. Once normal air is mistakenly used with it you must for safety reasons have it cleaned and serviced. Don't let this happen to your nitrox dedicated equipment. Have Nitrox Tank Valve Cap installed on all your cylinders used exclusively for nitrox diving and there will not be a costly mistake made. Giving you scuba cylinder assembly the proper care it deserves includes protecting the valve. This vinyl protective cover for scuba cylinder valves fits standard yoke scuba cylinder valves, not DIN scuba valves. The cover helps prevent impact damage to valves. Helps keep dust, dirt, and water out of scuba valves while preventing loss of O-ring. Valve cover is useful for identifying cylinders and is also the standard to let boat and dive operators know if your cylinder is full or empty. Place cap over valve when full and leave off when you need a gas fill. Cap comes with black nylon string, unattached.