The Sennheiser 55640 is a 1 pin Lemo connector, for example as a spare part for Sennheiser MKE microphones. The workability is very fiddly, you really need a steady hand to solder the jack. There is no strain relief and the cable breaks very often. Therefore you cannot find these connectors with recent products (Sennheiser used to provide some of their bodypacks of wireless systems with these connectors in the past). Unfortunately there's no other and cheaper alternative to repair some old microphones.