If you purchase a CURVE by 4SCORE, this Magnetic Ring 2-Pack is already included. These will screw onto any 510 cartridge to easily connect your cartridge to the CURVE battery magnetically. This also makes it simple to switch between two different cartridges. If you need extra magnetic connector rings for your CURVE, we offer back-ups! These magnetic rings are designed specifically for the CURVE by 4SCORE, and always come in a pack of 2.