Great question! This is best approached with good CAD and a good drawing:

1. CAD – design your hole or boss feature with the recommended drill diameter for the insert. This will be larger than the tap drill size since it accommodates the insert. Make sure it’s the drill diameter so there is material to cut threads into (I just recently saw someone accidentally design to the major diameter and get surprised when their inserts just fell through the hole)!
   1. Please give extra clearance below the bottoming depth of the threaded insert! Or else you risk installation that is above-flush with the surface.
2. Drawing – this is where you call out the threaded insert (helicoil, KATO, etc.):
   1. Add a BOM or note with the part number of the insert you called out and how many are needed.
   2. If ambiguous, add an isometric view or call out to show the direction of installation (more common in sheet products with a thru-hole).
   3. Minor countersinks are nice on holes with threaded inserts to remove burrs.
   4. On your arrow call out you can say “DRILL AND TAP FOR [SIZE OR P/N] HELICOIL INSERT”
   5. If there is a tang, you should call out in the notes to remove the tang.
   6. I like having a call out on notes to install sub-flush, e.g., [TOP COIL TO BE 0.75 P TO 1.5P BELOW SURFACE]. P is pitch, so imagine you’re installing at least 3/4 threads below flus but no more than 1.5x threads.

For more reading you can look up your helicoil and you can usually find a nice guide like this one: https://www.stanleyengineeredfastening.com/-/media/Web/SEF/Resources/Docs/Heli-Coil/HC-2000_rev11_web.pdf