Folks peddling old spark plugs on eBay usually fail to specify what base a plug has, and the pictures are often inadequate, but they often give the number of the plug. I know that the two-ground Edison plug for Model T use is #13. What other Edison plugs, if any, are also for Model T?
The single ground plug for a T is a #14. It burns hotter than a Champion X.
And it's cousin is the Splitdorf 775.
Right on guys........ I'm running Edison #14's ... even put a set in the '22 Touring at the Thomas A. Edison Estate Glenmont in West Orange, NJ