The problem most folks have with cage nuts is that no one ever showed them how to install them properly.
I think I’ve seen most of the mistakes people can make with cage nuts, though I learned long ago never to say I've seen it all, as someone will come up with an even worse idea than the ones you've seen.
The biggest mistake you can make is mounting the cage nuts on the front side of the rails.
If the nut is on the front of the rails, the weight of the gear that nut is supporting is borne by the spring tabs, not the nut and bolt themselves. If that gear starts to pull the nut out at all, the top clip will come out, and the gear will fall out of the rack to the floor.
With the nut on the back of the rail, the tension of the bolt itself pulls the nut into the rail hole, making a much more secure connection.
Then we come to the great horizontal vs vertical debate. Though I've been unable to find a definitive best practice on the Internet, each approach has its advantages; I'll switch back and forth as the situation requires.
The horizontal mounting model -- which places the spring tabs of the cage nut on the sides, not the top and bottom, of the square hole -- has the advantage of easier access when installing and, more importantly, removing the cage nuts, since you only need access to the sides.
The problem with the horizontal method is that the cage around the nuts is frequently too big to allow nuts to squeeze into all three holes of a rack unit. At least for the cage nuts we have around the lab, the tabs that hold the nut into the rails stick out a bit less than the ones that hold the nut into the cage, so vertical mounting works better for rack units that need all three.
Everything's easier with the right tools
I can't count the number of times I've walked into a client's data center and seen their folks installing and removing cage nuts with their bare hands. Think about it. The spring that holds that cage nut in the rack has to hold around 50 pounds; squeezing it in takes a significant amount of force. Add in that the cage around the nut can be sharp, and cage nuts end up being a continuing source of minor injuries.
The funny part is that most of them have one or more cage nut insertion tools, but they've never been shown how to use them. Most server cabinets come with an insertion tool that looks like someone bent the blanking plate for a PC expansion slot.
Unfortunately, many of these little gems get lost or thrown out. I keep them hanging on a hook in the lab and have even bent and filed down a PC slot blanking plate when needed in a pinch. You can buy a fancier one with a plastic grip from Server Racks Online for $15, or you can find them in combos with cage nuts and screws on Amazon.
Installing a cage nut with the insertion tool is a snap -- just stick the cage nut in the hole, hooking one of the cage nut's tabs into the rail. Then stick the skinny end of tool through the hole along the opposite edge, with the hook facing in. Grab the inside edge of the spring clip with the hook, and pull as shown above. Viola, the cage nut is installed -- and no busted knuckles, cuts, or dented thumbs.
Next page: Removing cage nuts