This section is a general guideline for fastener distributors, fastener manufacturers and users to select and specify platings or coating treatment to provide corrosion resistance. Each specification is detailed in the following format:

1. Plating/Coating
2. Color
3. For use on
4. Corrosion resistance
5. Characteristics

After careful review, work with your supplier and plating/finisher to determine which plating/coating will provide the desired results. Testing is highly recommended!

1. ANODIZING
2. Frosty — etched
3. Aluminum
4. Excellent
5. Acid electrolytic treatment for aluminum, frosty-etched appearance. Hard oxide surface gives excellent protection. Can be color dipped after anodizing for preferred finish. Used on threaded parts and fasteners, particularly for aircraft applications.

1. BLACK CHROMATE
2. Black
3. Zinc or cadmium plated steel
4. Additional corrosion resistance
5. Black semi-lustrous. Chemical dip used for decorative outdoor purposes. Can be lacquered. Suitable for identification of threaded fasteners by coloring. Chromate can be supplied in red, blue, green, olive drab or other colors as may be needed by the application. Chromate reduces oxidation of base plate and provides mild corrosion resistance. Treatment is soft and not resistance to abrasion. Surface scratches easily; careful handling is required. Color fades when exposed to sunlight and water.

1. BRASS
2. Gold, iridescent
3. Steel
4. Fair
5. Uniform appearance. Makes a serviceable decorative finish when lacquered. Economical. Plating is soft, not resistant to corrosion or abrasion.

1. BRONZE
2. Copper/orange
3. Steel
4. Fair — indoors
5. Color similar to 80 percent copper, 20 percent zinc alloy. Electroplated with lacquered finish for recommended use only indoors as a decorative finish.

1. CADMIUM/ELECTROPLATED
2. Silvery-gray
3. Most metals
4. Excellent
5. Cadmium was at one time a widely used plating, particularly with socket screw products. Today government restrictions limit its use, because it is toxic to the environment. Cadmium provides a high degree of corrosion resistance, particularly in salt atmosphere. Because of lack of resistance to abrasion, not recommended for threaded products subject to frequent cycles of tightening. Some anti-seize, anti-gall, and lubricating properties. Plating is smooth and uniformly deposited with good appearance. A supplemental wax coating is often added as a lubricant when cadmium is used on prevailing torque locknut. Limitations of cadmium include that the plating is soft, not resistance to abrasion. Limited porosity resistance under .0002 plate thickness. Contaminating qualities prohibit use in food processing and packaging equipment, although it has been the coating of choice for aerospace and marine applications or other critical or corrosive environments. Usage is controlled by government priority during national emergencies.

1. CLEAR CHROMATE
2. Clear bright
3. Cadmium or zinc plated parts
4. Very good to excellent
5. Clear bright or iridescent chemical conversation coating applied to zinc or cadmium-plated surfaces for added corrosion protection, coloring and paint bonding. The colored coatings usually have greater corrosion resistance than the clear. See Black Chromate.

1. DICHROMATE
2. Yellow, brown, green or iridescent
3. Cadmium or zinc plated parts
4. Very good to excellent
5. See Clear Chromate

1. CHROMIUM/HARD
2. Gray matte
3. Most metals
4. Good
5. Seldom used for products due to high cost but recommended where fasteners are frequently adjusted. Provides a most durable plate with high resistance to abrasion. Excellent wearing qualities. High resistance to seizing and galling. Low coefficient of friction. Thicker platings (.002 or more) subject to peeling, or flaking under impact or bending.

1. COPPER
2. Copper — matte
3. Most metals
4. Fair
5. Excellent lubrication where maximum torque values must be obtained without risk of seizing and galling. Especially well suited to applications where heat is a factor. Flash thickness provides good base for other platings such as cadmium, nickel, zinc, chromium. Smooth, uniform deposit and appearance. Excellent electrical conductivity. Economical. Low abrasion resistance. Color oxidizes and darkens with time, can be used for antique, statuary and Venetian finishes.

1. BLACK OXIDE
2. Dull black or luster black with oil dip
3. Ferrous metals and stainless steel
4. Fair
5. A chemical discoloration which does not add to part thickness. Usually combined with an oil dip. Rust resistance comes from the oil dip. Provides a uniform black finish. Best used indoors, outdoors poor in regard to corrosion resistance.

1. LEAD
2. Matte - grey
3. Steel
4. Fair to good
5. An economical finish which provides superior corrosion resistance against acid fumes, corrosive liquids, etc. Has good anti-seize, anti-gall and lubricating properties. Facilitates soldering, plating is soft, not resistant to abrasion. Toxicity prohibits use in food processing and handling equipment. Applied by hot-dip method.

1. NICKEL
2. Matte or bright (silvery)
3. Most metals
4. Very good
5. Used principally on many products where decorative appearance, combined with excellent wear resistance, is required. Provides greater resistance to abrasion, somewhat less resistance to corrosion, than cadmium due to high porosity. Hard surface. Standard finish on cap nuts and countersunk finishing washers. Relatively expensive and sometimes hard to apply.

1. PASSIVATING
2. Bright to matte
3. Stainless steel
4. Excellent
5. Chemical treatment. Removes iron particles by dipping in nitric acid and products a passive corrosion resistant finish.

1. SILVER
2. Matte to bright
3. All metals
4. Excellent
5. Provides finish suitable for special applications of many threaded products in instrument and electrical controls. Gives superior electrical conductivity. Resistant to seizing and galling at higher temperatures. Reduces friction of sliding parts. Soft deposit. High cost is a limiting factor of use.

1. TIN/ELECTROPLATED
2. Grayish-white
3. All Metals
4. Excellent
5. Recommended for many threaded products where anti-seize, anti-gall qualities are required together with resistance to corrosion. Tarnish resistance to organic acids.

1. ZINC/ELECTROPLATED
2. Bright or bluish-white
3. All metals
4. Good
5. Today’s most popular plating for fasteners. However, requires a thicker plating to equal corrosion resistance of cadmium. Smooth deposit, uniform appearance and good adhesion to base metal. Very suitable for post-plate treatment. Some lubrication, anti-seize, anti-gall qualities. Plating is economical, soft and not abrasion resistant. Tendency to stain or discolor when handled. Plating thickness not as uniform as cadmium on long lengths. Limited porosity resistance under .0002 thickness. Some electrical resistance. It is recommended in many applications to add a clear chromate treatment for additional protection against white oxidation spots which can form due to moisture. It is also recommended by certain industry experts that case-hardened parts which are electroplated should be baked after plating to minimize the risk of hydrogen embrittlement.

1. ZINC/MECHANICAL
2. Dull — grayish
3. Most metals
4. Good
5. Mechanically applying zinc to fasteners reduces the risk of hydrogen embrittlement forming within the parts. This minimizes the need for the precautionary practice of baking the parts soon after plating. A clear or bluish chromate finish is applied on top of the zinc to provide additional protection against white oxidation spots which can form due to moisture. It is common plating on spring steel split lockwashers and socket screw products.

1. BLACK PHOSPATE/OIL
2. Black (dull or bright)
3. Steel
4. Good
5. Anti-chafing properties used on sliding or bearing surfaces. Black manganese-iron phosphate coating with non-drying petroleum oils containing corrosion inhibitors. Standard finish for most drywall screws, particle board and retaining rings; while grade GT locknuts, spring nuts are supplied with an additional oil finish. Colored phosphate coatings are chemically produced which will increase corrosion resistance. They provide superior corrosion resistance to oiled surfaces.

1. HOT-DIP GALVANIZED (ZINC)
2. Dull grey
3. All metals
4. Very good
5. Hot dip galvanizing is generally the most effective way to apply a sufficient thickness of zinc to threaded fasteners for the zinc to serve as a corrosion protectant in harsh environments. During the galvanizing process, steel reacts with molten zinc, forming layers of zinc-iron alloy which are metallurgically bonded to the steel surface. This hard barrier has a low corrosion rate and resists mechanical damage. Corrosion resistance is directory proportional to coating thickness. Size must be adjusted to allow for thickness of coat. Nuts are re-tapped! Commonly used on fasteners used in construction (A32 5 structural bolts) or bridge and dock fasteners (carriage and lag bolts).

1. DACROMET
2. Silver — various colors
3. Most metals
4. Very good
5. A leading inorganic metal finishing system recognized as a proven and cost effective alternative to both electro and mechanical plating. The coating compositions are proprietary water-based coating dispersions containing metal oxides, metallic zinc and aluminum flakes. The zinc and aluminum platelets align in multiple layers forming a metallic silver gray coating which becomes totally inorganic after curing. Dacromet provides an excellent barrier, galvanic action, passivation and self-repairing. Excellent resistance to solvents, electrical conductivity and a base for most paints, including electro deposited paint.

1. BLACK ZINC
2. Black
3. Most metals
4. Very good
5. Black zinc is very black, smooth and shiny. It is scratch resistant and protects parts better than most other forms of zinc plating. Outstanding salt spray tests. Considered an excellent plating for the color black — much better than black oxide.

1. TIN — ZINC
2. Silver — grey
3. Most metals
4. Excellent
5. Tin-zinc was developed to provide at least similar performance characteristics of cadmium plating. Because of the "carcinogenic" label placed on cadmium, Tin-zinc actually outperforms cadmium. Tin-zinc being 70% tin provides ductility and lubrication capabilities. Tin-zinc is growing in popularity and requires any plating supplier’s attention.