When the connector of duct/FCU/whatever is moused over and you right-click, selecting "Draw Duct" reads the properties from the connector so the duct is sized/placed/formatted accordingly.
It would be nice to have an option below Draw Duct that would say "Draw Fitting" and would only show relevant families. E.g. I select the end connector of round duct, right-click and then select Draw Fitting... in the Type selector, rather than having a list of relevant objects together with 99.9999% irrelevant ones, I would only have those that can be fitted directly to that connector, so picking up the
"Round End Cap: Standard" would be easier/faster.
If, I didn't want that pre-selection to occur, the current method of selecting "Duct Fitting" from the Mechanical Tab of the Design Bar would _fit_ the bill nicely.