The 39-01-3123 is a 12-way 2-row Mini-Fit Jr.? Male Plug Housing made of nylon. It mates with 5557 receptacle housing. The crimp housing is suitable for power, wire-to-board and wire-to-wire applications. This 5559 series plug housing can be used with 5558 Mini-Fit? male crimp terminals and 30490 Mini-Fit? male grounding crimp terminals.