The older 510 system has tapped holes for mounting the rails. The instructions for the older system states to drill these holes with a 9/32" drill bit. For starters, I didn't have a 9/32" drill bit, which surprised me, as I have a fair number of bits laying around. None of my sets contained that one, they just skip right over it. But I get it, make the holes bigger and unthreaded so you have room to adjust the rail position precisely using the guides, and make any alignment adjustments in the future.
However, as I played with it a bit, I noticed that the supplied screws fit into the tapped holes just fine, and that my rails were seating right up against the guides anyway. Moreover, all of the tables / rails ended up this way--that is, the holes drilled in all the tables seemed to be a perfectly consistent distance from the top of the table, or "perfectly" enough. And, to be honest, I would expect nothing less from ShopSmith.
So I ended up skipping the hole enlarging step and just attached the rails as-is in the tapped holes (still using the washers and lock nuts, etc.). As I mentioned in the other thread, everything seemed to line up great when installed, the connecting tubes worked 10x better than they did with my 510 system, the table tops were aligned, the rip fence rode along all four tables without catching or having issues clamping down on the "seams" between two of them. My thought process was, given the above alignment being good enough for me, that leaving the tapped holes meant it was a lot less likely that these rails could go *out* of alignment. I know if you tighten them down, they should stick pretty well, but if they get knocked by something heavy or accidentally dropped or whatever regular life things happen--I could see the rails going out of alignment if you had that play in there. I feel like this way, I've eliminated that possibility.
Here is where you all (that means you, Dusty) tell me I'm wrong and why and why I need to remove all the rails and re-do things according to the letter of the law. Go!