120mm Extractor Fan Duct for 100mm Outlet

In my workshop I fitted a 100mm (104mm outer diameter) outlet for connecting my portable air-conditioner unit to.  However, I wanted an extractor fan for when I'm laser engraving to help exhaust any smoke or fumes to the outside.  I created this simple duct which utilises a 120x25mm 12v fan, and it works perfectly. 

You will need 4x M3 heat inserts (with 5mm outer diameter), 4x M3x30mm bolts and 4x M3 washer.

I have included the STEP file should you wish to make any modifications.