Does it look something very much like this?
This is a PJ-051 connector (I believe you said yours has a locking screw-ring at the body?)
Then my friend what you have here is a "ground crew headset" - this is the headset the ground crew will use to plug up to the aircraft. The single plug makes this easier. A common return 'signal-ground' is used for mic and headphone, hence only 3-conductors are used (mic+, headphone+ and common signal-return).
What you need is a S830 to PJ055B/PJ068 adaptor. The S830 mates with the PJ-051.
Couldn't find one in a quick search on the web (I think David Clark makes one...), but your local avionics shop should be able to knock one up.
- GY