When it bottoms out on the inside hex the depth is perfect.
is that flush with the gimbal? does the cable thread all the way in or is there a certain depth the cable nut must sit at?Here you go 39/64 drill bit ..6094 , 1/4 inch pipe coupling, 1/4 x 18 NPSF tap , Red Loc-Tite.
With 1 hex machined off, the O.D of the sleeve is .619 leaving a .010 press fit. Once installed tap it thru if preferred but only a 5/8ths depth is needed for the shift cable threads
If needed PM me if you want it done
The new coupling
After some machining
Installed