I feel like this might/should exist, but I can’t find it. Is there a program that allows for replacement screw cap generation by simply entering a diameter, depth, thread gap, and thread pitch? Would be really nice to have something like that. I the meantime, maybe I’ll consider printing tpu corks/ stoppers with mid diameter equal to vessel opening diameter.
Don’t know about specifically for your use case of only caps, but all of the major parametric modelling programs have custom thread generating functions. Including FreeCad, if you want to pay $0 for it.
If you aren’t fussed about the end result looking fancy, you can just make a cylinder and whack a threaded hole partially through it in about three steps in FreeCad, and just print the result.