For future reference, here is how to determine the pitch of an unknown internal thread. Take a wood pin that is a little larger than the minor diameter and shave off three flats, leaving it triangular. Screw it into the hole and then unscrew it. Now use a pitch gage on the wood. If no pitch gage, then use a steel scale and count threads over a distance. I use a microscope for small pitches. Estimate the major diameter of the hole and use a table of standard thread sizes to see what standard diameters match the pitch. If you are experienced, the trick will also work on special threads.
Larry