thread tpi

Hello hobby machinists! I've been making changewheel charts, skip the next two paragraphs if that's all you're interested in. I want to cut a 2BA thread on my ML7 because I'm finding the allen bolt which is used to engage and disengage the back-gear is turning out to be a nightmare to reach...

Good Morning, Was wondering how does a machinist decide what tpi thread to use for a particular job. Currently in my head I see things as follows Fine threads - used for both measuring tools and fastening i.e. at 40tpi 1 full turn = 25 thousandths so fairly easy to graduate a dial into...