Fair Radio has some nice heavy duty units for $2.50.
I use the same type in my strapping tuner.
I have often had to make them. If I need really strapping ones, that gives me a good excuse to fire up the lathe. I have had to make some odd ones ova the years. 1/4" on one side and 3/8" on the otha.
If you make ur own you can use some nice strapping setscrews instead of the wimpy ones that usually come in the factory made unitz.
The Slab Bacon