This is part of a serial adapter kit that I use for troubleshooting Suns and other older equipment . I already had a usb to com adapter for my laptop but I needed various null modems , gender changers,db9to25 adapters to complete the kit. Monoprice had it all in stock and it helped me in troubleshooting at our data center.
I use them to connect a Cummins ECM interface to a laptop. OE replacement cable is about $40. At this price, when a mechanic abuses the cable and causes an intermittent connection, I just throw it away and get another!