That's strange... I wonder if there are different revisions of the 846 with different screws? I just spent a few hours today completely disassembling an 846 to clean it out. Those 2 backplane screws on the side of the chassis were exactly the same as the 3.5 hard drive screws, along with many other screws that attach to the chassis; I threw them all together in the same mag tray and didn't have an issue.