Perfect for clipping onto a backpack, purse, or key ring, this rugged aluminum pen features the legendary Fisher Space Pen ink. Able to write upside down, under water, over grease, and in extreme temperatures, it is a pen you can count on to work when you need it—whether you're braving the wilds of a national park or your morning commute. It can write over 12,000 feet before running out of ink, and it has an estimated shelf life of 100 years.