Here is a handy adapter that will allow a TENS unit with ordinary TENS pin leads to be converted to a 2.5mm audio jack adapter.  This adapter cable allows you to plug your TENS pins into the sockets of this cable and plug any 2.5mm electrode into it.  Many Rimba and Zeus electrodes have a 2.5mm male connection wire “hard-wired” to the electrode.  This cable makes is easy to use these electrodes and plugs.