These cartridges are used with the Regenpen.  I sell it separately in my store along with skincare bundles and other Lorde + Belle Products. ****BUY 2 GET FREE BOOSTER, BUY 4 AND I WILL INCLUDE AN ADDITIONAL FREE SERUM*** 15 Silicone RegenPen nano tips designed for first time use or those with sensitive skin. Cartridges should be replaced after each use. Each silicone tip measures at .04 mm. This means the depth of absorption of products that go into your skin. With this cartridge, please note that it's safer to leave on one spot of your skin for 3-5 seconds due to the gentle silicone tip pressure. Use the Repair Serum or HA3 for optimal results.