The M3 nuts have to be placed inside the slot where they will attack to the hard drive cage with the pointy side of the nut pointing up, not the flat top pointing up. You just take a hammer or something heavy and gently hit it until it sinks in all the way. Now, you can just mount the hard dive tray using a standard M3 bolt. Requires 4 M3 nuts and 4 M3 bolts.