The cap for this exciting Space Pen model is an actual .375 H&H Magnum Rifle Mag Shell. What a special gift for the hunter or outdoors enthusiast Inside is a Copper Zirconium Nitride Space Pen.When closed, the 375NS Cartridge Pen is the perfect size to carry in your pocket, purse, car glove box, organizer or toolbox, they will write upside down - at any angle, under water, through grease, extreme temperatures -30 to +250 degrees F, on almost any surface, three times longer than the average pen, and of course in the gravity free vacuum of space. The pen can stand up on its flat end as well, making it a great conversation piece to place on any desk. When opened, it extends to a full sized, evenly balanced writing instrument. The Bullet's timeless styling has been the topic of many art books and magazine articles. Often imitated but never duplicated, the Fisher Bullet Space Pen continues to be the most popular pen. PLEASE NOTE: We recommend that you never fly with your .375NS Cartridge Space Pen, the TSA sometimes won't believe it's a writing instrument And we want you to enjoy your Space Pen for a long, long time.