This is an adapter which allows you to use the Atari-Compatible joysticks
on your Ti-99/4A.
Simply hook up to your Ti-99 joystick port and plug in 
your Atari compatible joystick
We recommend the competition pro and Zipstick as the best
joystick of this type.
This is the 1 port version, we build this adapter in-house .
Check out our other Ti-99/4a items for Sale

Texas Instruments Ti-99/4A Joystick Adapter 1 port version