3.5 mm TRRS plug (CTIA)

Four-conductor headset plug in the CTIA pinout: tip left, ring 1 right, ring 2 ground, sleeve microphone. The older OMTP pinout swaps the last two, which is why a headset can work on one phone and not another.

Contacts

Position	Name
1	tip
2	ring-1
3	ring-2
4	sleeve

What it mates with

Mating is directional, so the two lists below are genuinely different: a TS plug in a TRS socket and a TRS plug in a TS socket short different things.

3.5 mm TRRS plug (CTIA) used as the plug

Partial fit

3.5 mm TRS jack

A headset plug in a stereo socket.

shortThe headset plug is one contact too long: its ring 2 and sleeve both bear on the jack's sleeve, shorting the microphone line to ground. Audio plays; the microphone is dead and its bias supply is loaded.

3.5 mm TRRS plug (CTIA) used as the receptacle

Nothing recorded with this connector as the receptacle.