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4-40 is bigger than what I normally use. For the triples I am making my own they are equivalent to your 3-56's. The smallest bolts I have made were 16BA which is the same sort of size as your 000-120. What is nice about making your own is you get a nice unthreaded shank with just the right amount of thread There must be an on line model engineer supplier in your country that will do you what you need. In the UK I would point you to EKP .Jo
4-40 is bigger than what I normally use. For the triples I am making my own they are equivalent to your 3-56's. The smallest bolts I have made were 16BA which is the same sort of size as your 000-120. What is nice about making your own is you get a nice unthreaded shank with just the right amount of thread Jo
There must be an on line model engineer supplier in your country that will do you what you need. In the UK I would point you to EKP .
I've never heard of 000-120. I know watchmakers use very small threads, but I don't know what they are. Do you thread your 000-120 with a die or a threading plate?
But Mr Silky reminded me that he is more than capable of threading down to 250 Tpi
250 TPI is a threading rate not surfacing. Jo