This was a quick design for a 40mm fan mount for the Ramps 1.4 board. Depending on how good your printer is, you will probably have to file out the grooves on the legs to ensure a good fit. *Update 7/3/2013 The infill percentage doesn't really matter as there isn't much in the object, so there won't be a lot of speed gains. I just attached the 40mm fan with M3 10mm screws, or you can use longer screws and nuts for a more secure fit.