Originally Posted by
Tourist in MSN
Thorn used to rate their heaviest duty rack with a higher rating if you used 6mm bolts instead of the more common 5mm bolts. In other words, the bolts were the limiting factor. Unfortunately I do not recall the numbers that they claimed.
And, weight ratings do not take into account the potholes or other road hazards.
The M5 bolts (grade 2, not stainless) are rated to something like 2000 pounds of sheer stress. It's been a while since I looked it up, but I'm sure it's orders of magnitude above touring loads.