A double top _________ is the top member of an interior partition.

The term "double top plate" refers specifically to the top member of an interior partition. In construction, a double top plate is used to provide structural integrity at the top of a wall frame, where the vertical studs meet. It is constructed by nailing two pieces of lumber together, which helps distribute loads more evenly and allows for easy attachment of the roof or ceiling structure above. This design also facilitates the installation of electrical and mechanical systems, as well as providing a robust boundary for the layout of the entire partition system.

In this context, a beam typically refers to a horizontal structural support that spans an open space, while a stud is a vertical framing member, and a post serves as a vertical support that could carry a load from above but is not specifically related to the partition itself. The focus on "top member" clearly indicates the importance of the double top plate in framing walls, making it the most fitting answer.