that is used as a way to push the logic board out the back. all you do is 1. make sure the back of the mac mini if facing you. 2. make 100% sure that you have got all the screws ( the tear down missed some screws). 3. make 100% sure that you have disconnected everything (i broke the clip to my IR sensor by not paying attention) 4. put two screw drivers in the holes and pull towards you
I took mine apart and tried to fit a 1 tb hard drive in it. it was a tight fitjust to get it into the correct place and when i tried to screw on the airpor metal mesh thing. it would not fit at all. in the process i broke the clip for the ir reciever (if any body knows where i can get one of these that would be great. and the screw part to were the metal mesh screws down to the case (it just popped out). so in short answer, no 12.5 mm height hard drives.