The Uwell Crown 4 IV replacement coils by Uwell are made specifically for the Uwell Crown 4 Sub Ohm Tank. The Crown 4 coils by Uwell offer a highly advanced atomizer technology, featuring SS904L material, double helix mesh design with a self-cleaning technology. The Uwell Crown 4 coils use SS904L Surgical Stainless Steel wire wrapped around 100% Organic Cotton giving you the richest flavor possible.