Uwell Crown 4 Coil Line. 1 x Uwell Crown IV (4) Tank. 2mL Standard Glass. In addition, within the atomizers is the patented Pro Flavor Core Optimization System, or Pro-FOCS for short. Furthermore, the Crown 4 has a visually striking design, being hand-polished and knurled at the top and bottom ends, making airflow manipulation and unscrewing of the top fill system even easier.