@radehi A type of trilobular thread rolling screw. It would be very difficult to design for manufacture even if I had a swiss-type lathe in house. It really should be rolled. Designing or making the rolling die plates is also not trivial, and I don't have access to a machine that could use them.

@oskay Hmm, want to roll the threads are going to use to roll more threads? On much softer metal, maybe? I thought that for a thread rolling screw you'd have to harden and grind it rather than just rolling; EDM or ECM might be an alternative to grinding.

@oskay My thought is that if roll threads onto screw A, are only work-hardened, not case-hardened or precipitation hardened or anything, so using screw A to roll threads onto screw B will probably damage the threads on screw A, unless screw B is really hot or soft brass or something. And trying to heat-treat or case-harden screw A after forming its threads will distort it unacceptably. But I don't know much about this stuff, so I'm probably misunderstanding something basic.

@radehi What is your goal with this discussion?

@oskay I'd like to understand what the relevant difficulties are so that someday I can solve them.

@radehi I would suggest that you first learn about the types of screws, what they are used for, and the manufacturing processes that are used to make them.

@oskay Thanks! Any information in particular you've noticed I'm missing from the last time I studied that? I could start there.

@radehi You might want to look at how screws are made, generally speaking.

@oskay Is surprising to me you would think I haven't looked at how screws are made, generally speaking, when yesterday was talking about relative advantages of rolling, grinding, and EDM for making hardened threads when lathe is no option

@radehi Yesterday you were suggesting rolling screws against one another was somehow part of the process. And you were suggesting grinding and EDM. So, yes, that is what I would think.

@oskay Oh, I wanted to say, except through-feed dies, a cylindrical or planetary thread rolling die has threads on it, so is itself a screw. Assumed by "trilobular thread rolling screw" you meant such a thread rolling die, so the question was how to make the die with limited equipment. Was puzzled at the idea of trying to make such a die by rolling!

In how much grinding and EDM, grinding is already common for hardened ballscrews (maybe forgot about ballscrews), and EDM tapping is already common, so clearly EDM is an option for making threads, though don't know of anyone using it for outside threads now. Obviously is not competitive for volume production.

Now see that meant https://taptite.com/assets/files/taptiteii-conti-reminc_5.pdf the which is a self-"tapping" machine screw with a non-circular cross-section. ("TRILOBULAR" is a trademark.) Seems like rare geometry is principal problem, together with surface finish.

The REMINC brochure emphasizes the need to request the brand name from distributors, so maybe are selling generic manufacturers clones of off-patent REMINC screws under different name. The brochure also gives geometry pretty detailed. Fascinating product, thanks.

@oskay Guess you deal with a lot of early learners, no? Appreciate you being willing to offer me advice, which would have been good for an early learner!