This jacket serves as a holder for a slim WD HDD.This thing makes a tight fit with the second hdd-bay on the caddy created by 3dGringo.DL from here: http://www.thingiverse.com/thing:410048The stl file does not include the small opening for the usb-plug on its specific position. This may be a different size and position on several  hdd's , so cut it out with a sharp knife.