Help with those thread cutting nuts on emblems.

So on the 66 dart sedan, which just got painted. Some of the letter emblems had been glued on, due to stud being gone.
I bought new (used) emblem letters and the studs are well worn. I bought a supply of thread cutting nuts, like the ones that are OEM. For the 1/8in stud, but due to some of the studs being already worn and cut, I cant get any bite with the new nuts. I tried wrapping the stud in electrical tape, and no good. Does anyone have a fix to get these new nuts to go onto the old worn studs???