The SMRectangularBranch sheet in the HVAC.xls workbook defines the surface mounted components with rectangular nozzles that you want in the Catalog.
Type the part number for the round branch. An example is SMRectangularBranch1.
Type a description for the object.
Type the face width of the damper for the object.
Type the face depth of the damper for the object.
Type the component type for the object.
Type the symbol definition for the round tee.