How to know the inner diameter of a threaded hole


I have a question about the threaded hole and the chamfer in the attached blueprint.

From what I know the isometric thread, M4*0.7, should be 4mm in outer diameter and 3.3mm (4mm-0.7mm) in inner diameter. Does this mean that the hole should be 3.3mm in diameter?

Also, how do I know what the chamfer should be according to the blueprint?

Thanks in advance.

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1 Answer

The Process of the Threaded hole is done by first making a hole and then using Tap threads on those holes.
In first step there will be a 3.2mm hole for M4.
In 2nd step usually 3 taps for M4 tapping are used on drilled hole.
Later the chamfer you see is applied for deburring the sharp edges from the result of drilling and thread tapping.

The main purpose of the chamfer is to avoid sharp edges. Also the internal hole for the thread can be 3.2mm or even upto 0.3mm larger depending upon the strength of joint required. I have seen 3.8mm working for M4 Threaded hole which doesn't required additional strength(cover).

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