This is a hot-swap drive cage, I designed it to hold 4x 2.5 inch drives, each up to 15mm thick. I made this for my old 2u server I emptied out, which doesn't have its own 5.25 slots. However, I sized it to fit in a 5.25 bay so it could be useful for others. Keep in mind there are no ready-made holes for mounting it to one, so you might need to craft your own setup for that.

My infill was 5%, the trays were printed with supports for just the bottom of the handles. The cage doesn’t need supports, but needs to be printed vertically, front facing up.

You won't need a lot of hardware for this project, just some screws for the drives and the connectors for the drives themselves. I also thought about keeping things cool, so there are plenty of holes all around the casing for air to flow through.

The holes at the back are for a SFF-8482 29-pin connector cable, the kind commonly used with 4x SAS cables. I used a particular one that you can find through this link. To secure it, I slotted in the drive first and then glued the connector in place. Personally, I found hot glue to do the job well, but you may want extra strength if you don't want to worry about the connector coming loose later on.

Note: the tolerances are very tight, so if you run into any trouble getting things to fit, you might need to do a bit of light sanding or adjust the print size. I didn't have to do any of that myself.

Known Issues:

Because the drive trays attach at the bottom rather than the sides, there aren't any guides to keep them aligned perfectly in the enclosure. Sometimes if you don't insert them straight, the back of the tray might tilt up a bit, missing the connector. This is unlikely to be a problem with 15mm drives, but I usually insert the drives at a slight downward angle to minimize the chance of that happening.