hi which of these fire extinguishers are safe? some look old and rusty and which of them can i use for a marble gun type thing like Brians?some dont look to have fittings i could screw oither fittings into.
theyre going for $1 on
http://www.trademe.co.nz 
NZ version of eBay for those who dont know what it is.
and you Aussie guys dont try and buy them theyre all mine

and the seller only allows pick-ups 8)