A Coupling Nut is just as described, it's simply a lot longer than a standard nut. So no drilling and tapping required as long as you get the correct thread. IIRC the set screw set me back about 23 cents and the coupling nut was probably 40 or 50 cents. Add in the 50 dollar Carhartt short sleeve shirt I picked up on the same trip and it only cost me 51 dollars to modify my trimmer to use a hand drill for power.
Note, I have an excellent local hardware store nearby that knows how to hit every single one of my buttons. First, the Floor Staff really knows the store and the various experts in the store. So, you not only get answers to questions, you actually get good accurate answers to your questions. Then they are a Spyderco and Benchmade dealer, a Carhartt dealer, and the owners taste for cashiers runs to attractive and friendly females. As a result I look forward to going there but tend to dread what that trip will cost me.
Yeah, I am bragging a bit. I feel that it's real unfortunate that the Big Box retailers have been so effective on killing off the local stores and avoid them whenever it's possible. Because I'm old enough to remember the times before Home Depot and remember the unique aroma of oiled wood floors and the rust preventative used in the nail bins back when I was a kid.