Headset Plugs FAQ
What is the difference between 2.5mm and 3.5mm audio plug?
Headsets with sub-mini 2.5mm plugs were previously used with cell phones a decade ago. They still may be used today with some cordless phones or office phones.
Simple way to determine, if you have 2.5mm or 3.5mm headset plug - try to connect it to either your computer audio jack, MP3 player or a smartphone. If it fits snug - it's 3.5mm plug, if it's loose - it's 2.5mm plug.
Headset plug with microphone or without? How to tell if it is headset or headphone?
Sometimes words headsets, headphone or earphone used to describe the same or different things. Usually they distinguished by the presence or absence of the microphone. If it's just "earpieces" - it's headphone. If it has embedded (or attached) microphone, it's headset.
So, when you look at the 3.5mm plug, there could be two options - 3x metal conductors (referenced as Tip-Ring-Sleeve or TRS) or 4x metal conductors (Tip-Ring-Ring-Sleeve, or TRRS). Audio piece stays the same between these plugs (Left ear, Right ear, and Ground signal), however headset has an additional conductor for the Microphone circuit.