A1 Coil: 0.17 ohm Single mesh coil with a very wide center hole for optimal airflow. Suggested operating range of 90-140 watts 0.17 A2 Coil: 0.2 ohm Dual mesh coil for superior vapor production. Suggested operating range of 50-80. A3 Coil: 0.15 ohm Triple mesh coil for superior vapor production. Suggested operating range of 60-100 watts. S1 Coil: 0.15 ohm Single mesh coil for superior vapor production. Suggested operating range of 40-80 watts. S2 Coil: 0.15 ohm Quadruple Kanthal coil for superior vapor production. Suggested operating range of 30-70 watts. K1 Coil: 0.2 ohm: Quadruple Kanthal coil for superior vapor production. Suggested operating range of 80-130 watts.