When recreational divers think of a bail-out bottle, chances are it’s the Spare Air 300 that comes to mind. Just 13 inches tall and two inches in diameter, the Spare Air 300 uses a balanced, single-stage regulator that screws directly onto the bottle. It stows in a custom holster that mounts to a BC, and can easily be deployed one-handed. The Spare Air 300 is always on, so it's easy to just put it in the mouth and start breathing. The 300 can be filled directly from the primary cylinder in seconds via a yoke adapter. It can also filled from a fill station or compressor with a special fitting. A built-in pressure indicator nub protrudes when the bottle is full, or you can get an optional dial pressure gauge. Easy to fill, stow and use, the Spare Air 300 is the perfect miniature redundant air supply system.