Black Oxide

Black oxide is a conversion coating used on steel fasteners that creates a thin, black surface layer by chemically reacting with the metal. Unlike plating, it does not build up a thick deposit on the threads, so it typically has minimal impact on dimensions and thread fit. Black oxide finishes are common on screws, bolts, and set screws where a uniform dark appearance and clean look are desired.

On its own, black oxide provides only limited corrosion resistance, so it is often paired with an oil or wax topcoat to improve rust protection and add lubricity for more consistent tightening. It performs best in dry, indoor environments or light-duty applications where appearance and reduced glare matter more than heavy corrosion protection. For wet, coastal, or outdoor exposure, stronger corrosion systems (like zinc plating, hot-dip galvanizing, or stainless steel) are usually a better choice.