The adapter plug connects Io to the remote-release socket of your camera. Io fires the camera through this socket, so your camera does not need Bluetooth. Camera brands use different sockets, so there is one plug for each type.
Type your camera model on the camera compatibility page. It shows the code of the plug you need. Choose the same code in the list above.
Plugs into the 2.5 mm socket of Io. The plug turns in the socket, so you can set it at the angle that fits your camera.