Tecmojo 1U Universal Rack Mount Rails,4-Post Server Rack Shelf Rail with 20.9"-32" Adjustable Depth Fit for Non-Rack Mountable Server/Networking/AV/IT Equipment

I guess technically you could mount it with just the four screws but with a full server and lots of drives in there, it will sag and be very dangerous. I do not recommend haha. If you do not want rails at all you can get a shelf with 4 posts or something like this as well: https://www.amazon.com/Tecmojo-Universal-Mount-4-Post-Shelf/dp/B0CJZP2QWJ I originally bought that Tecmojo shelf and while it worked amazingly I found out that my case wasnt able to be secured to the front of the rack with screws since the the shelf took up a lot of space. So I returned it and went with the sliding rails and am really happy.