Hello,

[dia sym]6.8 TAP THRU
[counterbore sym] [dia sym]16 [depth sym]4
M8 X 1.25 [depth sym]10

dimensions in MM

Does anyone know where I can find in writing what exactly this callout gives you for thread depth? Wether the depth is from the surface of the part or from the bottom of the bore?

I forwarded your question to a
journeyman machinist with more
than 40 years in the industry
and here is his verbatim answer :

When preparing ports or other female threaded applications the original datum / face is the determining factor for the depths of any & all depths, this includes tap drill depth, full thread depth & counterbore (s). You can find this information in the Machinery's Handbook

Here is a link to the homepage of the
company who makes the Machinery's Handbook.
If you do not have a copy of this book I
would strongly advise buying one as it is
full of standard machining operations. I
would not be surprised if you found used
copies for sale on someplace like E-bay
or Half.com

"Machinery's Handbook"