I'm somehow obsessed with the idea of putting more than four 3.5" drives into my Mac Pro. Right now, all four sleds are occupied plus there is one WD Raptor in the lower ODD bay (-> one onboard SATA-connector still available). My last idea was to use the case of an old CD-drive to mount two 3.5" HDs on it at right angle and customize the ODD sled to make the connectors accessible, so that the result would be similar to transIntl's Pro Caddy 2 (which is simply too expensive for what it does) Unfortunately, 3.5" drives are just slightly too long to fit into a CD-drive case at right angle... My current idea is to attach an additional drive to one of the drives on the sleds by connecting the two drives with two thin sheets of metal utilizing their screw holes on the sides (see attached image, just a sketch, not a masterpiece of art ). Now the question is whether there is enough room between the drive on the sled and the one on the next sled to fit in the metal sheet and a screw. I can't remember right now and my Mac is busy at the moment; it would be a slight pain to draw it out anyway, disconnecting all the cables etc. Does anybody happen to have their Mac Pro open right now to take an inspecting look...? Or any experience concerning such enterprises – I mean except using cable ties , this is not about mounting an SSD but a full-grown hard disk.