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Wiktionary
mechanical pencil

n. (context US English) A pencil with a replaceable and mechanically extendable lead that wears away with use, designed to provide lines of constant thickness without requiring sharpening and typically features a small eraser at the end opposite the tip.

Wikipedia
Mechanical pencil

Mechanical pencils are used to provide lines of constant width without sharpening in technical drawing and in writing quick neat writing. They have also been used for fine-art drawing.

Mechanical pencils were first used in the 18th century, with many designs patented in the 19th and 20th centuries.