Black oxide (also known as bluing or blackening) is a chemical surface treatment. Steel fasteners are immersed in a high-temperature (typically >100 °C) alkaline solution containing oxidizing agents (e.g., nitrites).

Zinc electroplating uses electrolysis: the fastener (cathode) is placed in a zinc-ion solution, and an electric current reduces zinc ions to deposit a uniform pure zinc layer on the fastener surface.

Hot-dip galvanizing (HDG) immerses cleaned and fluxed steel fasteners into molten zinc at 420–530 °C, forming a metallurgical bond. The resulting coating consists of zinc-iron alloy layers covered by an outer pure zinc layer.

Dacromet is a water-based, chromium-free (early versions contained chromium) anti-corrosion coating.

Teflon coating uses polytetrafluoroethylene (PTFE) as the key component. It is applied by spraying, dipping, or composite plating to form a functional organic layer on the fastener surface.