The Basics (continued):
More rubber grommets? Wonder what they can be for? Well one of them is giving you a hint.
OK, I can't keep you in suspense any more (mostly because I doubt I ever did). Those rubber grommets are useful for passing your cables behind the motherboard tray and keeping the inside of your case neat, clean, and the air free flowing. The Cooler Master engineers even thought of putting eyelets for you to secure the cables to the tray. If you notice that sort of bare spot in the middle, that is a place to mount a 2.5" HDD. I have to admit, I'm not really sure why you would want to do that but the option is there for you if you choose.
Heck, they even thought of including the cable ties along with all the normal screws that come with a case. Really, these guys put some thought into this.
Here we get to see the rewards of running the cables all behind the motherboard tray. In all my years of building, I've never been able to make the inside of a computer look so clean with almost no effort!
Lastly we get to see what that large black box thing at the bottom of the case is. It's a cover! For all those nasty, but necessary, cables coming from your power supply. Now you don't have to worry about how long the cables are (assuming they are long enough of course), nor about spending the extra money on a modular power supply just to help keep your cables all neat and clean on the inside of your case.
They even included Molex to 3-pin fan converters if you need them. Also, if you see that little black dot, it's something that fell out of the case when I opened it. Doesn't seem to be part of anything I was able to find, and with all the other attention to details in this case I found it a bit odd. No big deal of course.