If you can find a open ended spanner that will fit in the slot neatly, then close an adjustable spanner (shifter) on the open ended spanner, turn the 'shifter' and the plug will unscrew, that will get you out of trouble. But what I use is a short length of flat bar, ground down and radius to suit the shape of the plug, then use a shifter on the steel flats, plugs always come out easy, cheers Dennis