The difrence between Novarossi ultra plugs is only the gold conector for plug warmer. and the difrence between novarossi long turbo plugs #tc or #tgc is the tapare at the very tip of the plug in a novarossi "Tc" plug that taper that seals the plug to the button is longer and on a difrent angle to the novarossi #tf or #Tgf short plugs. Normaly in the novarossi turbo plugs a novarossi 4tc 5tc 6tc and 7 and 8tc and tgc plugs are ment to be used for off road engines. Were as the novarossi 4tf 5tf 6tf and 7 and 8tf and tgf plugs are normaly used in on-road engines. Also a novarossi std plug is what i would call a long plug compared to an os std plug witch are very short. My rule is what ever engine brand you use you that brand of glow plug. Glow plug choice for running condishions and fuel type is vital to make the correct choice as it can have extreame difrences in how the engine paformes and tunes. Regards Jeremy.