You can use it for 1 drive,2.5" SSD or 3.5" HDD.Supports computer cases with an available 5.25 inch drive bay;allow to Mount 1x 3.5 - inch (or 2.5 inch or SSD)Drive and 1x 12cm fan.
Above Install hard disk , below install the fan. Make sure the hard disk high speed read and extend drive life.
when you install a fan, it will account more than a optical drive.
This adapter can adapts any 2.5" or 3.5" form factor drive to 5.25" drive tray.
Dimension 145 x 120 x 8mm(L x W x H)/ approx. 5.71 x 4.72 x 0.31 inch.