This window mount is for Wilson/weBoost Magnet-Mount and Mini Magnet-Mount Antennas. The 901128 is the latest version, replacing part 901118.
The window mount allows Magnet-Mount Antennas to be attached to a window or glass surface. It's particularly useful for moving an in-vehicle kit for use indoors in a cabin or trailer.
Suction cups simply attach to inside surface of window, and the antenna mounts on the horizontal platform.