[Formulajones]

Originally Posted by Scott65

I've seen it referenced both ways in regards to heat range... I chose the 6 for mine as an experiment to one heat range colder than the 3924 Autolite. It seems roughly correct for that. Heat mark about halfway down the strap anyways. FWIW

Yep I think we're on the same page. That's how I view it too, the 6 is one heat range colder than a 3924.

I see the 3923 and the "6" NGK as the same heat range or very close.