2.5mm TRRS vs. 2.5mm TRS

2.5mm TRRS adds a microphone conductor to the 2.5mm TRS jack, following the same CTIA or OMTP wiring conventions as 3.5mm TRRS. It served as a mobile phone headset jack -- including on older Nokia handsets -- before 3.5mm became the universal smartphone headset size.

2.5mm TRS is the smallest common member of the phone-connector family -- the same tip-ring-sleeve wiring as 3.5mm TRS, scaled down to a 2.5mm shaft. It was used for headset jacks on cordless phones, two-way radios, and early portable tape recorder remotes before 3.5mm became the standard smaller size.