This fitting is used to connect standard 3" air duct, as used for bathroom fans, to the poly sheeting used in inflatable greenhouses. It can be purchased, but is not readily available at most local suppliers, so I printed some.

To install, poke a small hole in the poly sheet. DO NOT CUT A HOLE. Poke a small hole through one layer and then stretch that hole out to about 1/2 the diameter of the fitting.

Tuck the notch into the hole and twist carefully until the flange is between the poly layers. This will stretch the poly around the fitting and form a seal. It works much better on a warm day. Blue vapour barrier tape is recommended to connect the hose and to avoid leaks around the flange.

I created these fittings to create a jumper between the two sides of my shed, as the non-blower side would lose pressure in cold weather as ice formed on the ridge. With the jumper installed, both sides are now properly inflated and shedding snow.