These fittings in the program are the same and have the same data group properties only with respect to size. The difference is what the program places with respect to the type of ductwork that has been placed.
Consider the example (above), when rectangular duct is placed, and when the tool is selected for transition “Rect to Round “is selected, the program responds properly and places the proper fitting( Upper) But with Round ductwork the program responds differently. When round duct is placed and when the tool is selected for transition and “Round to Rec “is selected, the program responds by placing the same fitting, but the square flanges of the fitting is connected to the round end of the duct. The fitting is placed backward. (see illustration above)
The proper way is that the fitting is placed in example, (Below), This choice involves a few more steps. The fitting has to be rotated and place on the ductwork with the flanges facing outward to allow the fabrication and connection of rectangular ductwork. (see illustration below)