I've modeled those legs, so I can wall mount my Mikrotik CRS326-24G-2S+RM. They are made for 4.5x40mm wood screws (I'll use wall anchors to mount them to a wall). The second pair of holes is to mount the switch securely to the brackets. They use M4 nuts & bolts, you can use any round head nut for the mount.

I suspect that this will work for any rack hardware, since the legs are usually the same, but please test it and give me feedback if possible. Also keep in mind the weight of your hardware. The Mikrotik weights in about 1.3kgs, so it's pretty light and the brackets will hold it no problem.