does anyone know how to "Be sure to shim your engine correctly. A plug that's too close to the piston can cause pre-detonation, which will quickly damage a glow plug."? Thats what it says on the os site for choosing plugs. Right now I'm using a medium traxxas plug on my lightning with two shims (i compared it to the stock plug on my lightning to the spare traxxas one i had and saw that it was too long so i added an extra shim to try to prevent the plug from touching the head). Is there any way for sure to know if the plug is touching? Is it ok that I'm using the traxxas plug? Should i switch over to the OS A3 plug? And can i use the OS A3 plug on my traxxas 3.3? Are they better quality than traxxas plugs?

I personally wouldn't do that. Especially using two plug gaskets. You take a chance of causing leaks and I have noticed when screwing in and out my plugs, the gasket will be thinner from tighening it many times. I would use the correct length of plug and only one plug gasket for your engine.
But that's just me.

I'm just a beginner so I don't know alot about shimming a glow pulg, but why would you take the risk on damaging the engine when you can just spend $6 or $8 dollars and get the correct plug? I have the tsunami uw and I run both the OS A3s and the OS #8s both have been excellent plugs for me and they aren't but $7 bucks. If I were you I'd just leave the Traxxas plug in your Traxxas and go get the short plug you need............just a suggestion........

thanks for the input guys. i did some more research and found that the washers are actually crush washers that collapse to make a tight seal so stacking them is not a good idea. i was just desperate to get another plug when the one on my lightning went bad because i wanted to run the engine dry since i was about to put it away. ill make sure i have extras on hand from now on. btw heres info from the traxxas forums that may be useful to people:

Crush gasket
New plugs include a copper washer to achieve a proper seal. They are designed to be installed with the concave side facing down, like an upside-down bowl. When the plug is tightened, the soft material flattens slightly and provides a strong seal. Never install the washer with the convex side down; it will deform and leak. It is also important to re-install a used washer the same direction as before; although it may look compressed, the side with the imprinted ring should always face up.