Open hole: 12mm.The all -in -one copper rod car is processed gold plating, the electroplating is bright, the contact performance is good, and the insertion is good.4mm jack, banana plug available.Taking one = 10 (including: 5 red+black 5), free shipping price: 18.80 yuan.Except for Hong Kong, Macao and Taiwan, Xinjiang, Tibet Autonomous Region and remote areas, other places.