KOSS THE PLUG SPARK PLUG SPARK PLUG with Mute Button This is a set. I have confirmed that the PLUG and SPARK PLUG with Mute Button are working. The left side of the SPARK PLUG did not produce sound. Hydrolysis and sun damage have occurred. There are areas where the logo has disappeared. The stickiness of the cables has improved slightly with anhydrous ethanol. I will also include the parts for the popular Gi-boshi (bullet connector) modification from back then. Please understand that the sound quality is very unique and that these are vintage items before purchasing.