We might want to mention that some engines are very glow plug sensitive. That is, some of the more seasoned pilots at your site may be able to let you know what brand and type of plug works the most reliably for each brand of engine and it's particular installation. I now from experience That sometimes a really hot engine with high nitro may burn out good plugs like OS #8's or A3.s, where as other less hot heavy duty plugs tend to last longer. That's why we have clubs, and find good mentors to keep us from having too many problems. If you are not sure and can't get the information from your club or LHS, Thank God for RCU, you can always post a thread on the particular problem you are having. We have all benefitted from just reading threads that might apply to our particular problem, then find the solution to a question already asked.