I want to build some sliding shelving. 80/20 will work great, but their rollers have no published load capacities, and when I emailed them they basically said they had no idea, but they didn't recommend putting more than 35 pounds on one of them. This seems incredibly silly as there's pretty much no way the $30 roller with the steel bearings has the same capacity as the $8 one with the bronze sleeve rubbing right against the plastic, but that's their script and they're not really interested in telling me where they source their bearings from so I can get more info.

So... anybody ever put more than 35 pounds of weight on one of these things and lived to tell about it?

https://8020.net/shop/40-2758.html

My plan is to distribute the weight across four per shelving unit, and I'm hoping I don't need to make that 6 or 8 as they aren't cheap. They will not be moved all that frequently, so most of the load will be static. 

I'm waiting on delivery of one so I can pull the bearings and see if I'd need to swap them and/or re-cast the wheels themselves in something more rigid.

I was planning on running bolts straight through the extrusion rather than relying on the T-slot for attachment, but the contact area should be substantively greater in either case given the size of the plate the rollers are actually mounted to. Whether or not the bolts on the wheels can hold is another matter I suppose.

Well your eyes are clearly better than mine because I can't read that at all!

That's about what I figured--there's no way the $20 difference in price wasn't buying a lot more strength.

Their limit might not stem from the bearing, but the roller on it (made from 'Nylon PA Glass Fiber Reinforced K222-D') which will concentrate the load onto a somewhat small area of it.

I agree, bearing is not the weakest link. Still, nylon is often used in casters. It should handle 100+ lb per wheel of this size.