While 2.5mm was the original standard for phone headsets, the slightly larger 3.5mm size is standard for music headphones and is now the more common size on phones. See: Headphone Jack (3.5mm ...

Using a female 2.5 mm stereo inline jack [octanechicken] was able to get the Xbox One headset controller to work with older Xbox 360 chat headsets having a male 2.5 mm plug. The photos on the ...