These Fan Ducts are designed to suit the "Olson Block", and will suit those that are running dual extruders, just mirror the LH Fan Duct. They also fit if using a Rear Fan Duct on the rear fan.The Fans are a slight push fit into the Duct so no screws required, they swivel on the rear print head assembly screws and latch on the front two.Once printed use a 3.0mm drill to clean out the mounting holes.The Ducts are fitted by removing the two rear print head assembly screws (long vertical Knurled) inserting the Ducts, add a spacer to the long screws and re assemble.(the spacers are to counter for the thread that extends through the bottom plate, which is usually about 3mm, fit if needed, adjust if necessary). If you add the spacers to the rear add them to the front as well.Once fitted the ducts can swivel out of the way to allow full accesms to the heater block ( Please remember to latch back into printing position before "Home Head" after maintenance) There are two different sets, one set has a notch (B,D,F) to allow more air flow towards the print nozzle the other set doesn't (A,C,E) the RH Duct has a few variants on shape.(I have only tested the A & B variants of the RH Duct) There is a great improvement on flow so you may need to reduce the percentage flow depending on the heater you are using. there is a 35W heater available from "3Dsolex" for those running the "Olson Block"Please let me know how you get on with using these ducts and any comments etc.