I have just come across some nos Champion 7-com plugs.
The T has Champion 20 plugs and my Hupp has Champion W 25 plugs. All the same thread. Are they interchangeable? Different heat ranges? They are made in Australia so I have no idea if the numbers are country specific!
IIRC 7-com plugs are 18mm thread, and uses a gasket. T plugs are 1/2" NPT thread.
Got it sussed! 3 very different plugs!