You will find that although threads are not listed under standard threading charts, doesn't mean that they do not exist.
A lot of specialist manufacturers use special threads, designed using standard thread formulae, to make unique parts. This helps them to keep control of spare parts, and charge what they want for them.
Once you have the OD, root dimension, pitch and thread angle, you can duplicate almost any specialist thread in existance, as long as your machine can give you the exact pitch.
On some German W+D envelope machines I used to work with, I made different sizes of taps for SAE (Society of Automotive Engineers) specialist superfine threads. Once you have they key to the threads used, you could very easily make up the special taps required. Thousands of squid to buy a new part, plus maybe weeks downtime waiting for delivery, or a few hours making a tap to repair the damaged part. You get a lot of brownie points with the boss if you can do that sort of thing.
This is one of those SAE taps, single flute, silver steel (drill rod) from many years ago. Plus of course, once you have the tap, you can make matching dies as well. They won't cut a lot of threads, but they get the job done at the time.
Bogs
