Weght limit for SolidSteel shelf/cones?

The aluminum cones will support the load. They are an aluminum alloy and are stronger/harder than the aluminum you typically think of. I have a 5.5 rack with a 2" thick maple top shelf with a VPI Aries 2 Extended. I don't know how much it weighs, but it is certainly more than 50 pounds. It has been there for four years without a problem. Don't worry about it.

Magister- I just placed the maple shelf on the cones, no countersinking. There's enough weight to hold it in place. If you do want to countersink the spot where the cones rest, put the shelf on the cones and position it where you want it permanently. Mark the cone locations then use a Forstner bit slightly larger than the size of the cone top to drill out the countersink. The Forstner bit is the only bit which will drill a flat bottom hole.