A 1" npt nut for a heating element won't fit through the top of a sanke keg. You would be much better off getting a solder on fitting for a triclamp, and then using a triclamp heating element.
I just use my vernier caliper to measure spark plug gaps. Nowadays they are pretty much good to go out of the box, unless you are really cheap and reusing a really old one or trying to diagnose something that doesn't want to run
Probably a bit late, but this link should help
https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.jbind.com/pdf/inst-tubing.pdf&ved=2ahUKEwim09uTyM_fAhWCL1AKHcKqB7sQFjABegQICBAB&usg=AOvVaw1AkH9lWiLAe35ig3HYfRO2