The Ninja Magna Cap is a magnetic nozzle protector for use on your HPA air tank. This nifty device protects your air intake nozzle from damage with its unique design. Magnet holds it in place for use on the field, and won't get lost during fills. Black color magnetic air nozzle cap is a MUST HAVE for all airsoft players. If you lose your crappy plastic protector, pick this one up, you won't regret it. We use them here at the shop with our personal guns.