There are two basic types of ball point pens: disposable and refillable.
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 apparatus, but other possibilities include a pair of buttons, a screw, or a slide.
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 apparatus, but other possibilities include a pair of buttons, a screw, or a slide.
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