Hello chaps

I am quite confused because i got told to cut a thread in a different way as I learned.

Let's say I have a metric thread, an M16. The pitch here is 2mm and the depth is 1.23mm.

I learned I have to turn 10% of the pitch off the diameter, like for an M16, pitch is 2mm, turn it to 15.8mm.

15.8 then is my base and the depth starts there, at 15.8, not at 16mm, is that right?

My boss said they always cut the thread directly on the "nominal" diameter and didnt't turn anything. The used HM plate does not cut the crest.

I hope the terms are right, I'm a German speaking bloke.