It depends on the device. I'm not aware of 5.25 inch bays, but they may well exist, I don't know. 3.5" are common, though 2.5" for laptop drives & SSDs are not unusual. The physical SATA power & data connectors are identical for 2.5" & 3.5" drives, so you can always connect a 2.5" drive to a 3.5" bay, it's just a matter of securing it. Some 3.5" bays have cut outs which can hold an 2.5" drive in place, or you can get caddies for a 2.5" drive to fit the larger bay.
Maybe you should describe exactly what you're looking for, or what problem you're trying to solve, and we can give some more specific suggestions/solutions.