by the look in your picture you are using fabrication MEP. Go to DATABASE>TAKEOFF>CAD SETTINGS>ANNOTATION. scroll down to the bottom you will see where it says Dimension Style. Whatever style is there is what controls your dimension on your duct work. Go to DIMSTY and look for the dimension style located in the CAD SETTINGS. there you can modify how to display dimension. What you are looking to duplicate the other guy is on the first tab in the DIMSTYLE suppress DIM LINE 1, DIM LINE 2, EXT LINE 1, EXT LINE 2.
WARNING if you use this DIMSTYLE for anything else it will change it for that as well. My Suggestion would be to create a new DIMSTYLE just for duct dimensions. Just make sure you put the name of the one you create in the CAD SETTINGS>ANNOTATION.
