Well, 16 Switchcraft 112APC Jack sockets wired together with 18swg tinned copper
wire, as four cascaded groups of four jacks. If a plug in inserted in the jack position
3rd, 5th and 7th on the right hand side, then this breaks the connection of that
group of mults to the jacks above. A simple and very useful utility module.
The Schaeffer front panel file for the mult is here.