Point of note......You can use any O.S. glowplug that suits your needs. We tend to use the O.S. #6 (old A3) or #8 glowplugs with no problems. In fact, we believe that the O.S. #8 glowplug is just about the best general-purpose glow plug you can use. With low-nitro fuels (0% or 5%), the #6 is a good one to try. We use O.S. plugs all the time and strongly recommend them.