Used to in- or decrease the diameter.
On the pictures you can see, which way you have to insert a y-piece on a tube fan. Both ends of the Y have to be connected with an aeration hose. In order to this you first of all mount the adequate ducting reducer, in case the diameter of the hose doesn't match the diameter of the y-piece. Ducting reducers from large to small (and vice-versa) are available in our online shop, too.
You mount the ducting reducer using a connector. The connectors, too, are available in different diameters, for they have to match perfectly.
They are important to keep the air from escaping at the interfaces of the system. Of course we sell these connectors as well. You will need another one to connect the y-piece with the tube fan. Enclose this interface with a tight connector as well.
After that you pull an end of the hose over the ducting reducer (IF you're using one, otherwise you pull it right over the y-piece). You have to fix the hose as well, of course. First to make it not slip, second to grant the efford of the tube fan. The best way of fixing the hose is to use a adjustable hose clamp. This fits on many different diameters. We sell hose clamps as well.
Well, you're repeating this with the second outflow on the y-piece and so the aeration can take place.