Not YOU again!!!!...........lol.........you still here!!.....lol.......Hi Fred!........your friend, Andyd........the petcocks sometimes freeze up, becoming difficult to undo, much better is to remove them entirely, they have either a 7/16th or 1/2" hex that you can undo them from the block and "free" the petcock up later, once removed you should have a stream of water run out but sometimes its clogged up with crud, just poke a piece of wire in the hole to clear it. As for the welch plugs they are 1 & 5/8th.......when I replace any that have rusted out I always use brass ones, never rust, ever.......and you can polish them, shiney.........makes the engine go faster!!.......lol.........andyd