DiversiTech 230-FR3, 3" SpeediChannel Flat Wall Escutcheon
 
Typically used to cover a rough opening in a soffit, wall, or ceiling penetration.
One side of the escutcheon is flat to allow for a SpeediChannel run going along a wall, and penetrating through an adjacent wall or ceiling.
This is the most common type of wall penetration.
Furnished in two parts, the escutcheon easily snaps onto the SpeediChannel.