The nuts for the L-iron top saddle bracket are a normal thread but it's a taller nut than standard nuts sold today. You can't tell from my picture but an original nut is in the middle, on the right is the "special nut" that I bought which is really just a nut that fits. It's about a 1/16" shorter and if you look at the back of the car it's more noticeable than in this picture. On the left is a lug nut that I just happened to find on a trailer a guy had used to haul some junk to the scrapyard and I stuck it in my pocket. The threads were the same and the flats were the same height as the original nut. I put it in a vice and ground off the taper part and it's hard to tell from the original. Those original nuts are hard to find without buying the whole L-iron, one of mine had a square nut when I got it. This is an easy, inexpensive way to get a correct nut.
Good to know ! Thanks for the tip Corey !!