--UPDATE-- there are 2 versions now; the original one which uses a ziptie, and now also one with an M3 bolt for a more secure and permanent grip on the hot-end.
Based on and remixed from the new Prusa i3 MK2.
I really liked the compact design of the fan duct from the new prusa i3 MK2, so I remixed it so it can be used on almost any printer with an E3D V6.
The E3D fan is the stock 30mm fan that comes with the E3D.
The layer fan is a 5015S 12V Blower, you can buy these almost anywhere if you don't have it laying around already.
20 % (doesn't really matter)
It's a print with a few overhangs and bridges, but any well calibrated printer should be able to print this.
I do advice printing it in ABS or PETG because it sits very close to the E3D heaterblock.