It's legitimate however I suspect an over specification given that the counterbore is specified with a very generous tolerance and MMC. Every hole - counterbore requires a new setup to measure and verify which is time consuming.
If the clearance between whatever and the counterbore hole is...
"dumb your drawings down for people who don't understand GD&T"
Then for whatever reason the wrong people are interacting with the engineering drawings. Train them, hire different people or utilize knowledgeable job shops.
As one of the following with the text "Minimum Full Thread"
- Append the thread specification with Depth symbol and the depth required
- Section view showing details of thread depth and drill hole depth
- Reference a note with the general thread callout (delta or flag)
Old guy here "USAS Y14.5-66" is short for: "United States of America Standard Y14.5-66". This was a publication of the American Society of Mechanical Engineers which was just a repackaging of ANSI Y14.5-1966.
Most folks back then referenced ANSI Y14.5-1966, eventually ASME gained traction with...
Double key, no but I assume you can just double the shear area for a close enough calculation.
I used these guys calcs recently. https://www.engineersedge.com/calculators/shaft_keyway_shear_and_yield_strength_15867.htm
SlideRuleEra, you should reach out to that guy over at Engineers Edge to measure interest - they publish a lot and have a bunch of old engineering archived books for free.
For thread stress see http://www.engineersedge.com/thread_strength/thread_bolt_stress.htm which has all of the equations for thread engagement per ISO 898-1, 1999 and FEB-STD-H28/2B, 1991.
Hope this helps
