DIR-1040SS, lets you fit 4 2.5” in a 5” bay.

Right, you may not have an urgent need for a 4 2.5” Rack bay in your computer, but if you are planning to mount a mini server, or have four 2.5” HDD laying around, or just want to build up the perfect RAID 0 setup (Via Software, or additional Hardware controller only) in the most compact case, the DIR-1040SS from Dirac is exactly what you are looking for.