I purchased these shelves for my server rack.
It's hard to write praise for a shelf. They fit the 19" wide rack without a problem. They can hold a lot of weight (I have a bunch of routers effortlessly sitting on a shelf). When I was installing a UPS, I mounted one shelf upside down and used it to hold the UPS while I bolted the UPS into the rack, then I was able to remove the shelf after the UPS was installed. (Simplified the installation since I didn't have to hold up the heavy UPS with one hand while trying to bolt it in with the other.)
The shelf contains a lot of air venting and various slits. I've been using those with tie wraps so that the routers on the shelf are not accidentally bumped off. They are also great for securing network cables.
When I need more shelves, I won't hesitate to get these again.
Brian J. 
