More than you probably wanted to know but

Acetal is the common name for a family of thermoplastics with the chemical name "PolyOxy-Methylene". Acetal is available in a general purpose
copolymer grade, a homopolymer version (Delrin ®), and several filled grades. Acetal provides high strength and stiffness, enhanced dimensional
stability, and is easy to machine. As a semi-crystalline material, acetal is characterized by a low coefficient of friction and good wear, high strength,
stiffness, dimensional stability, very low moisture absorption, good wear and abrasion resistance and a wide range chemical resistance.

Delrin is a Dupont version of Acetal with slightly different properties. Japanese companies love Delrin/Acetal and we used it for some extremely high precision gear trains. BUT our US customer made us use a different plastic and/or or limit the total amount per unit to XX grams or less because of its flammability. Its easy to machine, stable, low friction. All good. But the "flame and smoke" compliance guys for electrical equipment don't like it. It's not going to burst into flames on your lens or in your pocket, but in a fire large quantities can cause problems.