I can tell you that the Ninja glowplug is a wider taper than the Novarossi, and it will leave a small gap between the button and glowplug if you use the Nova plugs. I can only say to remove the button and try an O.S. turbo plug or O'Donnells and see if it is the correct size, since I know that the O.S. is a large taper glowplug. This is one of downsides of the Ninja engines, is you're stuck with their glowplugs and they are not cheap buying them in a single pack either.