Turn your Dremel into a blower or vacuum. It works really well!.75" ID output port, 2.15" inlet. Inlet bolt circle is 2.438" in diameter, and is for 6 4-40 bolts. Printed on a Fablicator! www.fablicator.comEDIT: The Impeller I believe is backwards. It still works very well, though. I'm going to re-print a mirrored version to see if it makes any difference. EDIT2: The impeller works about the same despite being right or left handed. go figure. Disclamer!!!Wear Safety glasses when first turning this on! The impeller tips spin at 200mph and will not hesitate to injure you if the impeller comes apart! Make sure the print is very good quality before spinning it up! Use at your own risk!Print all 3 pieces. Screw the neck onto the Dremel until snug. Thread the Impeller onto the Dremel shaft. It might be a little tight, but will go on with a little effort. It must be threaded on completely, so there is ~1/16" clearance between the bottom of the impeller and the neck. Be careful not to break the blades, though!Attach the shroud. The alignment pins should all line up and snap together with the alignment holes. Screw the neck and shroud together with (6) 4-40 X .25" screws.Congratulations, your Dremel is now even more multi-purpose!