CTEK Cig Plug is perfect for CTEK battery chargers with Comfort Connect, UC 800, us 800, MULTI US 3300, MULTI US 4. 3, 4. 3 Test & charge, 4. 3 Polar, MXS 5. 0, CT5 Time To Go, Multi US 7002. Note: The socket in the vehicle must be live when the ignition is in the “off” position to charge your battery using this accessory. CTEK Cig-Plug fits both 12 millimeter and 21 millimeter outlets and has a maze-like strain relief for the users safety.