This adapter will make it possible to connect 1 extra joystick to the PC. The gameport contains pins for two joysticks but you will need this adapter to be able to connect two joysticks to one connector
15 pin D-SUB MALE connector to the computer
15 pin D-SUB FEMALE connector to the Joystick 1 & 2
Note: Since pin 12 is often used for MIDI-signals on gameport equipped soundcards it's better to use the ground from pin 4 & 5, pin 15 is also used for MIDI-signals...
Источник: Tomi Engdahl"s Joystick page