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polyoxymethylene

n. (context chemistry English) A polymer of formaldehyde having a repeat unit of -CH2-O- ; it is used in engineering to make small gears etc

Wikipedia
Polyoxymethylene

Polyoxymethylene (POM), also known as acetal, polyacetal and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction and excellent dimensional stability. As with many other synthetic polymers, it is produced by different chemical firms with slightly different formulas and sold variously by such names as Delrin, Celcon, Ramtal, Duracon, Kepital and Hostaform.

Typical applications for injection-molded POM include high performance engineering components such as small gear wheels, eyeglass frames, ball bearings, ski bindings, fasteners, guns, knife handles, and lock systems. The material is widely used in the automotive and consumer electronics industry.