Use this attachment for your GS VV MOD system standard 510 thread . GS 2.8ML empty clear cartomizer/clearomizer 510 thread, it is same larger size of cartomizer in the GS Variable voltage MOD starter kits(4ML). It comes with 510 thread, which is compatible with Joye 510/eGo/eGo-T/eGo-C battery or USB battery/eVic. Simply remove mouthpiece to fill your favorite e-juices e-liquids with syringe ! It is designed to contain 2.8mL’s of e-juices or e-liquids, however, according to our experience, it can contain about 3 ml e-liquid. We don’t suggest over filling.