Duct Flange

My enclosure has a built in fan over an opening. I wanted to be able to control where it vents out to (a nearby window), so I purchased 4in ducting on Amazon. In order to secure the ducting in place, I designed and printed this. It is held in place using the screws that secure the fan to the top of the enclosure.The screw holes are 100mm apart and the holes are 6mm in diameter. The flange part is 100mm in diameter and 25mm tall, which should give enough space for 4in ducting to be placed over it