010-10121-00 Antena cable adaptador MCX a BNC MCX BNC GPSCITY ANSWER: Primarily when you want to connect any of the Garmin BNC type antennas (such as the GA26C / GA27 or the GA29) to your Garmin GPS unit that has an MCX connector for the antenna (such as the 12XL, 12CX, 12MAP, 175, 60, 76, 76CS, 76Map and eMap).