6 pairs of drive caddies. Used to swap hard drives. You could use these to boot a computer with different drives for different operating systems. Great for a teaching environment. Use for rotating offsite backups. Use for a media library. Archive media and plug in when you want access to the data. Keep those drives alive longer by not having them spinning when not in use. All worked when I was last using them. All for SATA drives. One bay is missing the door. I can include screws for the drives if you need them. They are of course interchangeable. You could install one Bay in your computer and use all 6 caddies to swap drives for that one computer. Let me know if you have any questions. If you have something interesting to trade like Star Wars LEGO, I might go for that. Pickup location is in Colwood near Dunsmuir Middle school. From a non smoking home.