This is the one I use for my GPS. It is a Belkin F5U109. It has the male connector for the serial part and nuts for your screws.
http://web.belkin.com/support/product/?lid=en&pid=F5U109&scid=1
I have the same intercom I purchased used with the 4 position add on box. Someone prior to me had lost the cord that connects the two pieces together. I called Flightcom and they shipped me a new cord for free. The next weekend I hooked everything up and tried it and it didn't work. After...