This quote was copied from the eBay site:
"...Invest in this Nice tool that will measure your Deck Height without removing the Head. Simply remove your glow plug screw in this Tool turn your flywheel once and Presto !!!! a precise method of measuring your Engine Deck Height. This tool will work on all .21 and .12 Engines using a Turbo Plug ONLY!!!! . If you have any questions please ask before you Bid."
Well, the picture shows a standard plug - the copy reads "turbo plug". I might be concerned - but, hell, it has a gauge...right? Oh, one other point - you have to remove the head button to set the zero point - okay, now I'm being picky...Like I said, it has a gauge.