This is a caddy for HP workstations Z600, Z620, Z800, XW6600, XW8600 or anything that has at least 2x5.25 spaces open. The caddy can be secured with the built-in latch, but it is a tight enough fit to secure itself by friction alone.
It can house 2x3.5+3x2.5 drives. 2 of the 2.5 drives can be SSD or HDD with 7-13.5mm thickness. The 3rd one will fit a 7mm SSD only.
I uploaded a raid version that will allow you to use additional 2.5 drives instead of the 3.5 ones or in any valid combination (9 x 2.5 drives or 5 x 2.5 drives + 2 x 3.5). If you don't use 3.5 drives at all, you have to use the 1-inch spacers to keep the original dimensions. You can get commercial brass M3 spacers or use 8xM3 nuts. I included a design here too that you can print as many times as needed. Use 30mm M3 screws inside the spacers.
The tolerances are wide so it can be printed on semi accurate printers as well, but as a consequence, the M3 nuts need to be glued in with epoxy. They won't pop in and stay in by themselves,
Needs 6x M3x35mm + 8x M3x25mm
Also, use an 80mm fan + fan grill +4 self-threading screws.
I did not use washers. The design is solid without them.