6.3 mm stereo (1/4-inch TRS)
Audio cables and connectors come in several standard sizes, which makes it easier for manufacturers to build new devices that will work with existing cables and connectors consumers already own. The 6.3 mm stereo jack, also known as a 1/4-inch phone jack or 1/4-inch TRS (tip, ring, sleeve) jack, is most typically used by professional audio components and other high end audio gear. Its smaller cousin the 1/8-inch jack or 3.5 mm connector is far more commonly used on consumer electronics devices.
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