Most electronic devices today have either a 3.5 millimeter or 2.5 millimeter jack designed for headsets, ear buds or computer speakers. Both of these jacks are miniaturized versions of the original 6.3 millimeter telephone switchboard plug. Since most computers and mobile devices use the 3.5 mm headset audio connection; most music headsets are manufactured with a 3.5 mm connector. When you buy a music headset for your mobile phone or other electronic device, take a moment to check that it has the correct connector for your device.
Jacks, Sockets and Plugs
The connector on the end of a headset is normally called a plug. Some people may refer to them as jacks, even though a jack is technically the the name of the socket half of the audio connector. The socket is the part that is built into the device into which the headphone plug is inserted. Jacks are called plugs because they "plug" into the device. The 3.5 mm and 2.5 mm jacks are also called audio, stereo, phone or headset plugs. The 3.5 mm jack is called a “mini” as in mini-jack or mini-plug, and the 2.5 mm jack is called a "submini” as in submini-jack or submini-plug.
The 3.5 mm jack is the standard size for music players, personal computers, mobile phones and other portable electronic devices with audio. The 2.5 mm jack is the standard for telephones that support headsets, including office phones and some cordless phones. Adapters allow a person to use both sizes interchangeably.
Both the 3.5 mm and 2.5 mm jacks come in two types: mono and stereo. If you look at the plug on a set of headphones, you can usually tell if it is mono or stereo. A mono plug has two contacts, divided by a narrow insulating band. The tip is the first contact, the black band is the insulator and the metal sleeve is the second contact. A stereo plug has two insulator bands and three contacts, the third contact between the two insulator bands.
The thickness or diameter of the 2.5 mm and 3.55 mm jacks is the only major difference between them. The 3.5 mm jack is approximately 1/8 inch in diameter. The 2.5 mm jack is approximately 3/32 inch in diameter. There is no electrical difference between the two jacks.