sydarm oring size

Hello guys,

Last time I played with my sydarm I blown the 2 orings (the white ones on the picture) of the CO2 cap.

I replaced them by some spare oringq I had for my shp reg but it doesnt't work fine.

Does someone can tell me the right size of oring i have to use ?

Thanks for helping me

http://i1078.photobucket.com/albums/...psb465c3f6.jpg