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Mechanical pencils have a metal or plastic (or wood) case. They use leads similar to those used in cased pencils. Mechanical pencils require no sharpening. The lead is forced out of the pointed end by twisting the cap, or by some other mechanical method. The lead rests inside a spiral (round coil) within the case and is held in place by a rod that has a stud (piece of metal) fastened to it. Whet the cap is twisted, the rod and stud move downward in the spiral, forcing the lead toward the point. Graphite for pencils is formed into spaghetti like strings, cut to precise measurements, and dried in ovens. Manufacturers vary the proportions of graphite and clay in the mixture to produce pencils with harder and softer writing cores. The Number 2 pencil is the standard and most common pencil used today. Pencils with numbers less than 2 have softer leads and contain less clay and more graphite. Soft pencils make a dark, heavy line. Harder pencils make a finer, lighter line.
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