I got dudded by an ebay seller in Melb when I got a packet of "O" rings from him, they were too thin and they would not seal up. When I bought all the primer caps and needles they came with "O" rings and I also bought another 50 or 100 from China and they were pretty cheap, can't remember the size but I wanted the thicker ones and they seem to work fine. I never reuse them,they always leak