BOX COUPLERS are predominately utilized in laboratory applications. 

ESI-310
Three Stub Box Coupler - BJ77 (3 lug) Connector
ESI-3210 / ESI-3310
Three Stub Box Coupler - internally terminated
ESI-3310R27
Three Stub Internally Terminated Bus Coupler that can be Switched out of the Circuit to Accommodate Testing.