FAULTLESS Tear Gas Cartridge PEN The patent number on the top goes back into the 1800s so I'm guessing that that is the patent for the firing pin mechanism.
This Tear Gas pen Works Perfectly. You would unscrew it and put a cartridge in. You then pull back on the metal end to Cock it. Then you Rotate the Pocket Clip to expose the firing Button and when you press the button it fires. This Pen is in Excellent Shape with No Flaws other than a Tad of Wear to the Body from being in a Drawer.