Wondering out loud - the leadscrew would be like a worm gear & therefore the missing threading gear would be a 'worm wheel'. And worm wheels are the funky tooth profiles with the angled teeth to match pitch, slimmer mid section, profiles as a function of shaft centers, typically made by hobbing etc. I've never looked that close at mine. Maybe its a glorified spur gear since its not really driving anything. Still, a spur profile would not really be meshing the leadscrew properly. It would be nice if you could get the real gear & make the housing/shaft around it.
