I added a good reference sheet to my photobucket album that you might find handy

Here is the [link=http://i231.photobucket.com/albums/ee247/jetpack_photos/Boards/ReadingGlowPlugsandHeads.jpg]link.[/link] It is too large to post here.

Running that high of nitro requires watching the head clearance as much as watching the plug. Once you have it sorted out, you shouldnt have to worry too much on them burning out on you, and be able to hang on to your spares a bit longer.[sm=thumbup.gif]