The 3.5mm headphone jack is an industry standard audio plug. Most commonly used for connecting a pair of stereo headphones to your smartphone or ‘piping’ your audio from your phone to an external amp either in your home or your car. 3.5mm headphone jack
Dependent on the number of connector rings, headphones can also include a microphone.
The exclusion of the 3.5mm jack is polarising with smartphone manufactures claiming that removing the jack saves space internally, allows for thinner phones while eliminating a potential ingress point for water.
The phone connector was invented for use in telephone switchboards in the 19th century and is still widely used.
The phone connector is cylindrical in shape, with a grooved tip to retain it. In its original audio configuration, it typically has two, three, four or, occasionally, five contacts. Three-contact versions are known as TRS connectors, where T stands for “tip”, R stands for “ring” and S stands for “sleeve”. Ring contacts are typically the same diameter as the sleeve, the long shank. Similarly, two-, four- and five- contact versions are called TS, TRRS and TRRRS connectors respectively. The outside diameter of the “sleeve” conductor is 6.35 millimetres (1⁄4 inch). The “mini” connector has a diameter of 3.5 mm (0.14 in) and the “sub-mini” connector has a diameter of 2.5 mm (0.098 in).