The Vape Safe fuse goes between the mod and the negative side of your 18xxx sized battery.
Due to the extra length it will add to your battery we can not guarantee it will work in all units.

7 amp Safety fuse for use in most mods.

With lithium batteries one of the biggest safety issues can come from a hard short.  The fuse is a mechanical fuse that will trip if it senses a short in the mod by breaking the connection to the battery.  While this is an extra safety feature is not a complete fail safe.

The VapeSafe can also help protect variable voltage circuitry in some devices, hot springs, and other circuitry in your mod that can be damaged from a short.