Speaking of half-nuts, I was measuring the pitch and diameter of mine for the very same reason, thinking I would copy them for spares. What I found was 16 pitch x .582 dia. Very confusing as .582 is just a shade under 15 mm and too fat for a 9/16 at .5625 .It's definitely 16 pitch and not 1.5mm a I used an optical comparator as well as a thread gauge. In my book the pitch rules, wondering what some of you others may have or know about them and what was the inch version lead screw pitch and diameter???