I forgot to mention that I have many 3/8-16 bolts in my workshop, and they are an excellent match when pressed together side by side with the bolts from the kit. No way I should be looking for something like 24 tpi. Also, there is a bit of variation between different nut/bolt combinations within the kit. And, with the kit bolts as well as with my 3/8-16's, in most cases it seems much harder to put the bolt in from the bottom of the nut. Maybe the kit manufacturer intentionally made the female threads to seize before they get in far enough to touch the bottom of the slot (and prevent the nut from sliding in the slot)? Come to think of it, when I use a second nut on the top of a bolt, I would probably be thankful for the bolt seizing in the lower nut. If this is the explanation, there still seems to be a case of sloppy tolerances in manufacturing...
