頭、環、袖，Tip-Ring-Sleeve

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Tip-Ring-Sleeve，TRS，係一種連接方法，分為2.5mm，3.5mm同埋6.3mm
1907年既一篇關於Triple Contact Plug既文章

TSR plugs

1. Sleeve: usually ground
2. Ring: Right-hand channel for stereo signals, negative phase for balanced mono signals, power supply for power-requiring mono signal sources
3. Tip: Left-hand channel for stereo signals, positive phase for balanced mono signals, signal line for unbalanced mono signals
4. Insulating rings

來源：wikipedia