If your HPA tank's fill valve is leaking you need to replace the seal.  These are properly sized and made of durable material that fist most valves including Ninja, Tippmann, Maddog, Iorman, First Strike, HPDMC, Empire, Genrics, Trinity, HK Army and Valken.  Auction is for 5 seals only.  We can send internationally for $1 more.  GOOD LUCK!