Any engine takes any glowplug as long as it screws into the cylinder head. All that matters is whether the engine runs smoothly. I start with medium plugs and adjust from there. I have two engines that take hot plugs, one is tiny (.08 cubic inches) and the other runs in freezing-cold weather. An engine that spends most of its time above 50% load in warm weather will probably need a medium-cold or cold plug, though a medium plug may assist with break-in to keep the engine running while the fuel mixture is rich. I prefer O'Donnell plugs, because the coils glow brighter than other brands I've tried (to help with startup), but they don't burn out any faster.

Don't believe anyone who tells you that you absolutely must run a specific brand of glowplug, or that you can never change the brand or heat-range once you've broken-in the engine. Nitro glowplugs all use the same technology, just use whichever brand is convenient for you to get your hands on, and figure out which heat range works best for your application. When you change brand or heat-range you'll need to double-check the engine temperature every couple minutes and tweak the fuel mixture as necessary for the first couple runs, but there's absolutely no reason you *can't* change plugs any time you want.