I am trying to change over 3 pin-lock kegs to ball type. I got the posts and they include the threaded portion that normally protrudes from the top of the keg. Everything went fine for 5 out of 6 posts but the threads on the keg for the last post must be worn or a slightly different thread size because the new post won't tighten properly. The guy who sold me the kegs said to just hammer out the threaded part out of the keg body and install one of the new threaded parts. Sorry this is clumsy - I don't know the right term for the threaded male portion of the keg. Anyway I'm a bit dubious about taking a hammer to the keg - it's not clear that this part is ever intended to come out - perhaps welded in place? There is rubber right up to the edge so hard to see how it is mated to the keg body. So... hammer or not?
I have never seen a keg where the threaded part was removable. If you got some out, they obviously must be, but I think you've run up against one like I've seen. I'd approach it differently....first, you can try to find an appropriately sized post by using this chart...http://www.ipass.net/mpdixon/KegThreadSizes.htm . Or do what I do...use threaded (flare) fittings (http://www.northernbrewer.com/shop/ball-disc-1-4-mfl-gas.html , for example) on your gas lines so you can just screw on the proper QD for either pin or ball lock kegs.