Unlike ordinary ball pens which rely on gravity to feed ink, the cartridge is pressurized. At nearly 50 lbs. per square inch, ink is continuously fed to the tungsten carbide ball, allowing the user to write at any angle, even upside down. The ink is also reported to write on wet wood, sap, bar oil, and even works underwater (for those really adventurous log builders). The Fisher Custom Giant blue ink with bold point. 4-3/16" long and .242" diameter. Works with Veritas scribers.