Fasteners are made from a variety of materials, including common steel, titanium, plastic, and others. Many materials are further classified into grades to describe specific alloy mixtures, hardening processes, and so on. Furthermore, some materials are available with various coatings or platings to improve corrosion resistance or change the appearance of the fastener.
Because of differences in strength, brittleness, corrosion resistance, galvanic corrosion properties, and cost, fastener material can be important when selecting a fastener.
Zinc-plated steel is a low-carbon steel for general use. Relatively inexpensive, with the zinc plating providing moderate corrosion resistance suitable for indoors or otherwise dry conditions. Color is either a blueish tint or yellow depending on the exact process.
Hot-dipped galvanized steel has a thicker zinc coating for better corrosion resistance, making it suitable for outdoor use. Because of the thick plating, only galvanized nuts and washers will fit galvanized bolts. The coating typically has a rough, dull grey finish.
Stainless steel offers good corrosion resistance, making it suitable for outdoor use and marine applications, but it is more expensive than zinc plated.
Chrome and nickel-plated steel are smooth and polished for appearance. The plating offers moderate corrosion resistance.
Brass and bronze are copper alloys with good corrosion resistance. More expensive than steel, these materials are typically used for decorative applications. Colors can vary significantly.
Alloy steel is highly hardened and usually black oxide and/or oil-coated, offering little corrosion resistance.
