Conical Tee

To insert a conical tee fitting, go to
Ribbon: DM HVAC→Ducts→  Conical Tee
Pulldown Menu: DM HVAC→Fittings→Conical Tee

You will be prompted to specify the duct on which a conical tee is to be inserted.

Select duct or label to insert fitting at:

A conical tee will be inserted on the drawing, as shown below.