3.5mm adapters were originally used in telephone switchboards in the 19th century, but have since evolved to be used with many audio devices. The tip, the ring, and the sleeve (TRS) each represent one of the contacts on the connector. Most times 3.5mm adapters are stereo, though, sometimes the adapters can be mono. You can tell the 3.5mm plug is stereo by looking at the connector. You see two rings, creating three separate sections. If there were only one ring and two sections, it would be mono. Stereo means the device uses at least two audio channels to direct sound to at least two loudspeakers. All of the 3.5mm adapters provided by FireFold meet industry standards for quality and come with our lifetime warranty.