Add grips on a duct object are used to draw a duct run, ensuring connectivity between the object and the duct run. Some fittings also contain add grips for creating a new branch from the fitting. For example, an elbow has add grips that let you automatically convert the elbow to a tee and then draw a duct run directly from the new tee connection. The existing duct branches remain connected to the other tee connections. The following illustrates add grips on duct objects.
From top to bottom: Add grips for a duct segment, an elbow fitting, and a VAV outlet plenum
Add grip used at the midpoint of a run to create a new branch run.
Add grip used on a connected 90 degree fitting to create a new branch.