https://www.thingiverse.com/thing:168750 is a lovely minimalist bracket to allow installing a 2.5" disk drive (e.g. sold state) in a 3.5" bay.

This remix adds:
-Slots for either hex or square thin M3 nuts. (Select the appropriate .stl file).
-Bottom mounting holes.

Print with fairly small layer height (I used 0.15mm).

Note: The side holes for the 3.5" bay are 60mm apart. Technically, these are not standard holes for a 3.5" drive. But they must be very common as I have checked them out on a bunch of hard drives and my PC case only offers holes at these distances.

See https://www.snia.org/node/4728: "Although a disk vendor may provide for three positions per side, systems manufacturers may find that the hole located between the two specified holes is not in the same location relative to the other holes for a wide selection of drives. For this reason, the middle hole has not been specified and is considered optional."

Drill out the bridges in the 8 3mm holes to allow screws to pass through.