http://www.justpaintball.co.uk/acatalog/Co2_Systems_.htmlhttp://www.justpaintball.co.uk/acata..._Systems_.html

20 oz = 0.56 kg ....You may well find ...as Mario says .... these more suitable for a feather.
Internal thread ...5/8 UNF...Tap/Valve thread 1/2 BSP.