I want to change out an old ball type end shower arm, but don't know what to do to remove the flange that's up against the shower wall. I don't see any screws holding it in place, & it's so thin that I can't get a grip on it to unscrew it. If I just remove the shower arm itself (see the post by "kebbin" from 1/31/08), will it just fall off, or is there something else I need to do?