Cabinet Cage Nuts by Linkbasic are fit for a 19″ cabinet, and rack.
A cage nut is used on a rack that has square mounting holes. You would use a cage nut when you need to mount a product in your rack that requires a threaded hole.
Although some modern rack-mount servers have bolt-free fitting, other components such as shelves, networking hardware, UPSs and KVM switches still tend to be fitted using cage nuts. Sold in packs of 4, includes screw and nut.