Does anyone know the thread pitch of a sparkplug for a '50 Flathead?

I am going to look at a '50 Mercury Flathead this Saturday. I want to do a compression check. I dont have a guage. All the dial compression gauge checkers I've looked at are metric.

The guy at Napa told me that the Ford V8 Flathead's are metric.

Is that correct?

Thanks

 

They are 14 mm same as my flathead V12 Lincoln.

Frenchy

 

Guess what plugs have been metric since the 30s in most cases.

 

I'm very surprised they would be metric.

Thanks!

 

Spark plugs were envented and produced first by Europeans. 14mm and 18mm are standard European sizes. I remember in the 50s that a lot of hot rodders insisted on using Lodge Spark Plugs.

From Inventors.com

Oliver Lodge
Oliver Lodge invented the electric spark ignition (the Lodge Igniter) for the internal combustion engine. Two of his sons developed his ideas and founded the Lodge Plug Company. Oliver Lodge is better known for his pioneering work in radio and was the first man to transmit a message by wireless.
Albert Champion
During the early 1900s, France was the dominant manufacturer of spark plugs. Frenchman, Albert Champion was a bicycle and motorcycle racer who immigrated to the United States in 1889 to race. As a sideline, Champion manufactured and sold spark plugs to support himself. In 1904, Champion moved to Flint, Michigan where he started the Champion Ignition Company for the manufacturing of spark plugs. He later lost control of his company and in 1908 started the AC Spark Plug Company.

 

and also factoid is that ford model T and such all employed a tapered thread like water pipe.