Sam;
I pulled the ball screw out of the junker. .522" x 22tpi. The diameter of the ball itself just ahead of the threads measures about .460", so I guess the ball size was what I was remembering as "About" 7/16" (.4375").
I, of course, do not know how Lefever threaded the frame but from being a machinist the thread has the features of having been tapped with what we today call a starter or taper tap. This will make a straight thread if run far enough in but would appear Lefever stopped short of cutting the full thread. This allows the straight threaded screw to start to bind as it enters the tapered portion or "Lead" of the tapped hole.
Taps today generally come in one of three configurations, starter/taper, plug or bottom. The taper tap has the longest lead or taper with the plug tap being a more or less general purpose tap. The bottom tap is normally used only following a plug tap when necessary to have full threads to the bottom of a blind hole.
This one is from an H grade SN 46,128. The other one I have measured was from an FE SN 38,025. I am positive they measured the same.
Do realize that after annealing & I assume re-hardening the screw may, or may not, seat to the same exact depth. The length of the bar may change a few thousandths.
