This is for the Roxon Flex multi-tool system.It’s a way to incorporate a tritium glow stick in to the scale (skin, covering) of the Roxon Flex multi-tool. The glow tube will glow continuously for about 12 years. You can purchase the glow tube on ebay (https://www.ebay.com/itm/335428114231?var=544832769885). This one is 3mm x 22.5mm and the only size that will fit this model.It is not super bright but you will be easily able to see your multi-tool in the dark. Once your eyes adjust you might actually be read something by it…..albeit very very close to it.I used a pause to insert light tube and then used transparent filament for the plastic that was above the tube.Enjoy, Tom