That plug is a tapered thread. Do what HRL recommends. If it still doesn't come out, hit the end of the plug with a number of sharp blows with a Medium Danged Hammer (BFH s overkill for this application). Being tapered, hammer blows have a tendency of causing the tapered threads to come apart. I don't understand why this is so, and I don't care if it turns out to be magic. It has worked for me.
Carl
