So it looks like 9.5mm does fit at least in the X220. I'm now almost certainly going to go this route instead of the Z5K500 since it gives the options of 640 and 750gb. 640gb 9.5mm drives are the same price as the Z5K500. There's only a .05 lb weight penalty and no power consumption difference. However, I just tried the method in the link above I don't like it. Good news is that a 9.5mm does fit fine in the bay and the cover goes on no problem. Getting the drive in is easy enough, but getting it out is a total b*tch. The drive goes in at an angle which means you have to push the hdd down with one hand to keep it from pulling on the sata connector on the systemboard up; this is fine. But when removing it, unless you have someone to push down while you pry it out the drive does make the connector on the motherboard deflect enough to make me nervous about doing this more than once. The root cause of all this is is four small tabs on the upper part of the chassis (facing down) where the hard drive cover goes on. I don't why they even bothered adding that as it does nothing (there are hooks at one end of the hdd cover, a couple along the line and the screw at the end). The fit is so close and tight that once I removed the stickers from the spare Seagate I had it's possible to slide the drive straight in. So the solution is to just file/grind down those four tabs and 9.5mm hdd's will slide in/out without any problem at all.