Rackmount label plate.

Place it on any empty 1U space of a standard 19" rack. Write on it with a magic marker to produce a label describing the rack-mounted device or a group of devices below it.

It can go to the front or the back of the rack, on the left or on the right. Just please make sure the one edge that does not have a fillet (i.e., is not rounded) is at the bottom of the label plate, not at the top. This is because the 19" rack standard requires the mount to be slightly shorter on the top than on the bottom (which effectively means the distance of the top hole from the top is 1/32" shorter than the distance of the bottom hole from the bottom). That leaves a little space between devices (as seen in the enclosed photo), so they do not clash with each other.

The label plate takes up only a small portion of the 1U space, so it does not interfere with the movement of the air between devices that suggest leaving an empty space below and above them (which just about all of them do).

I have enclosed the original rackmount.FCStd file, which you can open and edit in FreeCAD. If you want to make the plate longer, just change the value of length in the spreadsheet (called ss in the file). Or if you want it thicker or less thick, change the value of thickness. Do not change any values in the Side Strip section of the spreadsheet, as they contain the dimensions required by the 19" rack standard. Some of the values in the Mount section of the spreadsheet are not used yet because I made the file designing something else (which I will post when finished), but found the initial plate design useful in its own right for labeling my rack, and thought someone else might find it useful as well.

If you do not have FreeCAD (although it is truly free unlike a certain other CAD program that requires you to give them your email address and gives you a time-limited license they can revoke at any time), you can import the enclosed .step file to a CAD program of your choice. You will not have the convenience of just changing one or two parameters in a spreadsheet, but presumably you should still be able to edit the design.