Fine if you've got a lathe. I used the same technique that works OK with CRS rods from the hardware store. I did give up and buy a better 8-1.25 die. I am not about to contaminate my truck and car with with inch [censored]. I make my own muffler clamps. 5/16'' rod takes a good 8-125 thread. I thread the ends a length, bend it in a''U'' and reuse the saddles. When I roll under my truck, I know the 13 mm wrench will fit everything on the exhaust system.
Haven't touched the exhaust on my 02 Cavalier yet, but it too will get 13 mm nuts.