Spark Plugs 30' 40's

Are they 10mm plugs or 14mm and the length of the treads 1/2 inch"

I have some T8 10mm --- 13 universal --- 10 blue crown

14mm none

18 mm I have 88, 84 com, 85 com and there is a box of each

10mm sparkplugs were a big failure of the late nineteen thirties because of the lack of a space in-between the Insulator and the Inside of the outer body. They were used on Buick, Chevrolet, Hudson, Packard, Cadillac and other cars.AC-104 was one of the numbers! They were considered to a complete disaster by many people, especially by those who drove slowly and did not ?blow out the engine?. They would gather trash in the sparkplug and just short out.

Some had a reach of only ¼?.

Several places are on these posts if you care to look under 10mm sparkplugs. My guess is that most of the cars have drill and tapped out to 14mm, some manufacturers just changed the cylinder heads!

Some people might want the 18mm sparkplugs. A rather belatedly reply.

M. L. Anderson