Silver pen photo with handwritten text on cross section paper in the background
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More information about ballpoint pens:
A ballpoint pen is a writing instrument with an internal ink reservoir and a sphere for a point. The internal chamber is filled with a viscous ink that is dispensed at its tip during use by the rolling action of a small sphere. The sphere, usually from 0.5mm to 1.2 mm in diameter, may be made of brass, steel, tungsten carbide, or any durable, hard (nondeformable) material.
There are two basic types of ball point pens: disposable and
Disposable pens are chiefly made of plastic throughout and discarded when the ink is consumed; refillable pens are metal and some plastic and tend to be much higher in price. The refill replaces the entire internal ink reservoir and ball point unit rather than actually refilling it with ink, as it takes special high-speed centrifugation to properly fill a ball point reservoir with the viscous ink. The simplest types of ball point pens have a cap to cover the tip when the pen is not in use, while others have a mechanism for retracting the tip. This mechanism is usually controlled by a button at the top and powered by a spring within the pen body, but other possibilities include a pair of buttons, a screw, or a slide.
Rollerball pens combine the ballpoint design with the use of liquid ink and flow systems from fountain pens; Space Pens, developed by Fisher in the United States, combine a more than normally viscous ballpoint pen ink with a gas-pressured piston which forces the ink toward the point. This design allows the pen to write even upside down or in zero gravity environments. A graphite pencil can also be used in this way but produces graphite dust, requires sharpening, and is erasable, making it undesirable or unsuitable for use in some situations.