The Optimus 510 Cartridge is a replacement oil cartridge for your Optimus 510 Vaporizer. The convenient measuring scale lets you see the amount of oil remaining in your cartridge. The unique heating element in the chamber heats up your oils evenly and neatly. These cartridges are available in a pack of 3 and only in clear color. Contents: 3/pack Note: This item is only compatible with the Optimus-510 and eGo Series batteries.