PC expansion cards are secured by these handy little clips. They unlock easily when installing expansion cards, and snap down tightly finalizing your installation. External drives are secured by, what the manual calls, a screw-less kit. With the device in place, simply slide the "screw-less kit" into the locked position. Doing so forces two pins to protrude into the screw holes of your device, holding it securely to the inside of your chassis. Note that the hard drives are mounted transversely compared to the external drive bays. I’m a pretty big fan of this configuration and Sunbeam has executed it well.