What is the standard size for a D ring tab? Even those is the pic look tiny. 3/8" or 1/2" at most. I've used 5/8" but now I always go bigger.
I use 3/4" thick by 3" tall by 5" long. I use a 1" diameter hole and center it so there is 1" of steel all around the hole. I cut a hole in the front AND the rear of the tube, slide it through, bevel it a tab and weld it on the front and the back. I figured that was standard.