I am willing to bet there is some crossover to standard plugs in regard to how the body is shaped for heat retention, there just isn’t any readily available Information available. I have measured numerous plugs comparing the filament diameter and the size of the recess within the plug body. By far, the biggest difference in standard plugs is the size of the recess. Most glow standard plugs I measured had very similar size filaments. I’ll see if I can find my notes on the matter and I’ll post them.