Model A & B

Ford Garage

Spark Plug Tap and Die

Pictured above is a 7/8-18" tap. This is the original size of the spark plug threads in all original Model A and B cylinder heads.

Some late model replacement cylinder heads have been produced with slightly undersize threads, causing the spark plugs to be very tight and bind. I have used this tap to chase the threads on a couple of new heads for people. The spark plug should be able to be screwed in by hand.

Pictured above is a Pratt & Whitney 7/8-18" spark plug thread gage standard. This is useful to check the threads on spark plugs to ensure that they are properly sized and will not bind in the head.


More related information on Ford Garage:

  1. For more Model A & B related information, use the Site Search box at the top or bottom of this page.
  2. Model A & B 7/8-18 Inch Spark Plug Engine Lifting Eyes
  3. Model A & B 7/8-18 Inch Spark Plug Heat Ranges by Larry Brumfield

September 2016