This is the Futaba 6-Way SBus Terminal Box.

For use when S.Bus/S.Bus2 servos are used in the S.Bus system
Six ports, four in the center and one on each side
Receiver or S.Bus servo may be connected to any port

6-Way SBus Terminal Box with Extension Cable and Instructions

Terminal Box Dimensions: 1.4 x 0.50 x 0.59" (36.9 x 12.9 x 15mm)
not including mounting tabs
Cable Length: 3" (76.2mm) not including connectors