Understanding Fastener Platings and Finishes
Fastener Tech Data | Understanding Series Introduction
Platings and finishes affect not only how a fastener looks, but also how it will withstand corrosion—deterioration of the metal—caused by exposure to the weather or chemicals. Zinc is the most common because of its pleasing appearance, low cost and good rust resistance. Cadmium, once popular, is seldom used. Hot dip galvanized is very resistant to corrosion, but its finish is somewhat irregular and, consequently, unpleasing. Chromium (chrome), although expensive, is used when a bright hard finish is desired especially when the fastener is visible. Refer to the chart below for other options. You'll find all of the popular platings and finishes at Fastener Mart.
Finish |
Color |
For Use On (Material) |
Corrosion Resistance |
Characteristics |
|---|---|---|---|---|
| Zinc (electroplated) |
White to blue grey | All metals | Good | Most common used plating. Good rust-resisting qualities, appearance and low cost. |
| Cadmium (electroplated) |
Bright or dull silver grey | All metals | Excellent | Superior rust-resisting qualities used in marine and aviation applications. Relatively high cost and toxic to the environment. |
| Chromate | Yellow, olive drab, black, blue/white | Zinc & cadmium plated parts | Very good | A secondary dipping process after plating increasing corrosion resistance, adding color or brilliance. |
| Black Oxide | Black | Ferrous metals and stainless steel | Fair | A chemical discoloration which does not add to part thickness. Usually combined with an oil dip. Rust resistance comes from the oil only. |
| Phosphate & Oil | Charcoal grey or black | Steel | Good | Zinc or manganese phosphate used with a rust-inhibiting oil dip. Low cost. |
| Color Phosphate | Blue, green, red, purple, etc. | Steel | Very Good | Chemically produced coating superior to regular phosphate and oil. |
| Iridite | Olive drab, green, black, red, blue, bronze | All metals | Good | Applied on top of zinc or cadmium plating as a die for color and additional corrosion protection. |
| Nickel | Silver | All metals | Very good | Hard stable finish, relatively expensive and sometimes hard to apply. |
| Chromium | Bright blue/white | All metals | Very good | Hard lustrous finish adds wear resistance and is very expensive. |
| Hot Dip Zinc (galvanizing) |
Dull grey | All metals | Very Good | Parts are dipped in pure zinc. Gives maximum corrosion protection. Adds a thick irregular coating. Size must be adjusted to allow for thickness of coat. |
| Passivating | Bright - etched | Stainless steel | Excellent | Parts are dipped in nitric acid which removes iron particles and brightens the finish. Produces a passive corrosion-resistant finish. |
| Anodizing | Frosty - etched | Aluminum | Excellent | Acid dip produces a hard oxide surface. Can be color dipped after anodizing for preferred finish. |
Be sure to visit our Fastener Tech Data section for even more information.