This design was created because I needed to mount 4-5 disk drives in three 5.25" bay slots. With this design I have made it possible to mount any number of drives to five 3.5" disk drives and maybe more 2.5" drives if possible. I used the design of the intake fan for 120mm adapter from the below link to screw into. The files that are downloaded is the right and left side of the mount with the top being screwed into a 120mm fan and then into intake fan adapter.

http://www.thingiverse.com/thing:1373892
(I also attached my modified version of 120mm fan mount)

Used to screw in fans to HD mount.
6-32 screws --> length 1 1/4inch
M4 nuts

Used for the hard drives:
6-32 screws --> length 3/4inch
I also used rubber washers to help protect the hard drive vibration.

I have used this for about a month and it worked perfectly!
Hope you enjoy.

UPDATE

Still using this design for 2years and no issues at all!
Running Green and Red drives for my FREENAS and all drives stay around 30C.
Thanks for the support.

UPDATE

Updated the design when printing in ABS the hole for the nuts that hold against the fan and fan mount will shrink when printed. Made the size a little larger and cleaned up the design. Minor things I noticed after checking on the build after 2 yrs.