Fisher Pens are the ultimate in dependability. Environmentally friendly, Fisher Pens are guaranteed to perform in temperatures from -30 to +250 degrees F, underwater, in zero gravity, in elevations up to 12,500 feet, and at any angle. Each has an ultra-hard Tungsten Carbide ballpoint precisely fitted in a stainless steel socket to prevent leaks and deliver constant, uniform ink flow. Fisher pens use thixotropic ink (a semisolid ink until the shearing action of the rolling ball liquefies it) in a hermetically-sealed, pressurized reservoir with a sliding float to separate the ink from the compressed nitrogen. Lasting 3-times longer than ordinary ballpoints, Fisher Space pens are hand-tested and carry an unconditional lifetime guarantee.