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Tungsten carbide - is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms.
T 6099 (OTTO) Tungsten carbide, 0.1 - 5 µm, 99.99% Cas no 12070-12-1 - used to make the rotating ball in the tips of ballpoint pens, bridal jewelry, and gauge blocks, which is useful for producing precision lengths in dimensional metrology.