This adapter allows you to mount two 7mm slim 2.5" HDD or SSD drives in a 3.5" Slot.
The adapter has mounting points on the top and sides with the same spacing as 3.5" drives have.
Also there are holes with 30mm spacing as floppy disk drives use them.
The holes should fit for M3 Screws, to be screwed directly into the plastic.
For the 2.5" Drives you need four M3x12mm Allen screws.
Have fun.