This connects a standard 80mm computer fan to a 3" hose, and fits MakerBot M3 hex-head machine screws.
Print with a raft, to prevent curling. Screw the attachment to the fan (or other hoseless item), then attach a flex-hose with a hose clamp or zip-tie. Useful for venting MakerFumes out of your secret lab!
This is a fairly large print â€“ if you're printing on a Thing-O-Matic, check your G-code with ProcessingGCodeViewer ( http://www.thingiverse.com/thing:14980 ) to make sure you won't run out of space on the build platform. I had to disable the outline and reduce my raft margin.
For more details: http://zoomy.net/2012/01/30/thing-003-fan-attachment/