I have a ThinkStation ST550 that only came with 2 x 3.5" drive caddies. Instead of purchasing them for $12 each I decided to make some. There was a similar design for a 2.5" caddy, but I needed 3.5". So, with inspiration I came up with the design you see here. While I designed this to work in my ST550, I'm fairly certain it will work in other ThinkStation servers. It does not use a retention arm, it just has a small raised ridge that holds it in place.

I printed with:

• .28 layer
• 100 wall loops to make it solid and strong
• A brim to keep the long thin arms from warping and moving.
• I printed in PLA+, but PETG is likely in the near future because hard drives get pretty warm.
• You'll need low profile screws to hold the hard drives to the caddy.