Originally Posted by Oblarg

Really? That's somewhat surprising - in the past when I've used 80/20 to mount wheels, no matter how much I tightened the bolts the wheels eventually walked enough to loosen the belts. Admittedly, that was with plastic IGUS bearing blocks pressing against a t-slot, and not with aluminum plates clamping around a piece of 2x1, but I'd have expected the physics to be similar for similar-strength bolts with similar amounts of tension on them.

That said, there are holes in the VersaBlocks for mounting directly through the 2x1, right? So in practice you could simply slide the block until your belts are tight and then match-drill through the framing member and bolt it in place for all time. Won't work as well with chain, which expands, but with belt it should be a very good solution.