This interface converts the EM-400 mount head to the EM-200 mount head.
The Takahashi EM-400, EM-500, JP-Z and NJP mounts have a specific and robust system for fixing plates and dovetails using 4 M10 screws. If you wish to fix plates or dovetails compatible with the EM-200 mount, which is fixed with 2 M8 screws, the use of this conversion interface is imperative.
Diagram of the Takahashi EM-400 to EM-200 mounting interface