Rack mounting a 1U Dell Poweredge server, aka am I missing something here?

I have recently bought a used Dell PowerEdge 1950 Gen 3 server, nice little thing that we'll be running VMWare off for the office.

I bought the Dell ReadyRails rack rails to go along with the server so that I could mount it in our rack. Our rack is a Startech 4-post rack with adjustable depth and it has square holes that you put the cage nuts into to mount equipment.

I'm totally confused by these rails. The two ends seem to be able to "swivel" around 180 degrees, and the holes on either end is smaller than the screws for my rack.  All the videos I see online just say to "click it in" to the rack. That seems impossible.

Am I missing a piece of the rail kit or something or am I just not understanding how to do this?

Here's some photos of the rails so hope fully things are clearer.

Rail kit. The "Front" of the rails is on the left side in the picture
Closeup of front end of the rails
Close up of back end of the rails
Showing how the ends can swivelled 180 degrees when the tab is lifted. They can be positioned so the three holes are on the outside or the inside
So I guess my questions are - am I missing any pieces needed to mount this thing in my rack with square holes? What's the purpose of the swivelling and what orientation is it supposed to be in? And finally, how do I install these in the rack?
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I don't see anything missing.  You can use these with either racks that have punched out holes or pre-drilled.  I suggest turning both swivels so that the blue tab and hook are outside (I'll call it rapid-attach), then you won't have to use cage-nuts.  With the rapid attach out, that end mounts to the inside edge (front to back) of the rack post.  The blue part will be towards the bottom and goes through the bottom hole where a cage-nut would be of a 1U triad (for lack of a better term, the group of 3 puched out holes), and the little hook above it goes through the top hole.

Just snap one end onto the inside edge/face of a post, and then snap the other end onto the inside edge of the opposing post.  The hook takes the weight, and the blue tab is pretty much a quick release.

If you were to swivel both ends around, then you either need a rack with pre-drilled holes or you'll use cage nuts.  I don't use them in this fashion, but I believe it would just be a matter of threading a screw through a cage nut and into the hole in the rack end.  I think they still mount to the inside faces of the posts when doing it this way.
Frosty555Author Commented:
Okay so if I understand this correctly... I orient the swivelling things like this:

Closeup of rails with "rapid-attach" side out
The hook hangs on the top square hole, and the blue tab just goes inside the bottom hole? And then maybe put a screw through the hole in the middle? Does anything physically secure it the thing to the rack besides that? That seems so precarious!
The picture looks right.
Yep.  No screw.  That threaded hole is for the server - where the captured screw on the front panel of the server goes once you've slid it all the way in.

It may seem kind of precarious, but the rails snap into place, and with all the weight of the server it's not going to jump out.  I checked a few 1950s we have earlier just to make sure I wasn't forgetting anything, and they're all that way.

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