My BERCO tracks do have a flat surface for the nuts. Another trip to CAT and I obtained a bolt and nut with Mr. Magnet's part number. I brought it home and checked the fit. It looks correct to me.

Amazingly, (or - like everything else I found on this tractor) the bolts that were previously installed were at least 3/8 " too long in the shank. I doubt the bolt ever was properly tightened, and they probably used lock washers to take up the space. Also, this placed the end of the thread below the clamping surface to help lead to early failure.....

Here is correct bolt and wrong bolt pics