Hi everyone! I hope someone could guide me in the world of square thread machining and its tolerances/allowances. I got on old piece of pipe I shall find out what type of thread it has (most likely in imperial dim.) to be able to reproduce. Things I can measure: OD: ~136,2mm -> must be 5 3/8" TPI: 4 ID: ~130mm -> must be 5 1/8" Question part 1#: Now I have the Machinery's Handbook (29th ed.) and the only square thread ever mentioned in it is Acme square thread. But! a) Is Acme "square" thread actually has 5 degrees (or 95 if you call a square thread 90) and modified square thread has 10 degree with radial direction? Or b) Is Acme square thread really square and it has two modified "square" thread types: one is 5 and the other is 10 degree? Question part 2#: Is it axiomatic that?: pitch = 1/TPI hight of thread = depth of thread = pitch/2 Which adds up theoretically in my case too... Question part 3#: 2G, 3G, 4G tolerance classes. Are they valid for square threads? Where are these defined (for square threads)? Could it be correctly manufactured if I specify: 5 3/8" - 4 square thread - 2G Is this fully defined? And most importantly is this the thread I'm looking at? Thank you for you help in advance!