I built this simple stand to resistance check the center electrode values on some aviation spark plugs. The contact that goes into the plug is a piece of copper tubing with an insulator around it so it can't scrape the i.d. of the well and create a track of metal that could cause the plug to misfire. These plugs have not been "bomb tested" because as many experts have proven (and they don't all agree), a plug with a high resistance can pass a bomb test and still misfire. In my opinion, it stands to reason that if the resistance is high and/or the plug measures open, it will require more energy from the ignition system to fire it and that can eventually damage the ignition system as well as lead to intermittent misfires. While testing the old Champion plugs I found one that would spring up and down when I was pushing it against the copper tube. It turns out a few of the contact screws inside the barrel had backed out, one so far that it created the springing action. A couple of the plugs that were open had a resistance reading after the contact screw was tightened but they were very high. After seeing this "feature" in the Champion plugs, I opted to replace them with Tempest because, #1) they have a consistent, good resistance reading and #2) their design does away with the contact screw, the contact is fused in place in the barrel. I've read that Champion has changed their plug design and they now fuse their contact in place, like Tempest. Additional info here: http://blog.aopa.org/opinionleaders/2... http://www.qualityaircraftaccessories... http://www.tempestplus.com/Products/I... http://www.championaerospace.com/prod... Champion's spark plug maintenance video that addresses Tempest's statements http://www.championaerospace.com/supp...