Two hook-shaped pieces snap into a connecting bar. The short hook hangs on the back of the screen while the long hooks hold the external hard drive.
If you can spare the extra plastic, it would be better to print one of the hooks that is as wide as your external hard drive so you don't have to worry about the snap-fit connections. These connections are fragile. Also, your external HDD holder will be more robust if it is one solid piece without any connections.
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