Add washers to the underside of the bolt. Again, one inside the other. Thread on your nuts. I use two, one to go snug against the washers (not tight, it needs to allow the bolt to spin!), then another snug against it. Then loosen the first nut (the one on the underside of the...
Did find a nylon washer at Ace Hardware in one of the 100's of drawers of nuts and bolts and washers and knobs and etc. The one on the right fit right out of the drawer, but the hole was just exactly the size of the hole in the visual back (1-1/4"). Found the one on the...