Oops, the following helps you figure out if the socket is mono or stereo. Dir a plug, just look at it. Three connections = stereo, 2 = mono.
A mono plug plugged into a mono socket will have one connection of the socket connected to one connection of the plug, and another connection on the socket connected to the other connection of the plug. Any other connections on the socket are usually some form of switching, often opening when a plug is connected.
A mono plug connected to a stereo socket will have 2 connections on the socket connected to the tip of the plug, and another connected to the other connector of the plug. Again, any other connections are likely to be switch contacts.
A stereo plug in a mono socket will almost always have only two of the connections on the plug connected through to the socket. The ring will not be connected. If it is connected, it will be connected to the same connection as the tip. Again, there may be other switch contacts.
A stereo plug in a stereo socket will have three separate connections from the plug to the socket, with possibly some switch contacts.