What does the color of the screws indicate? It’s important to know so as not to waste money

Anyone who is not familiar with all the nuances of construction, when buying self-tapping screws, pays attention only to their size and thread pitch; but the color of fasteners seems to such a person to be a purely decorative parameter. Today we will figure out how yellow, white and black self-tapping screws really differ, because it is not without reason that they have exactly that color.

White screws

As a rule, self-tapping screws are made of hard grade steel. Initially they are light gray in color; It just so happened that in this case it is customary to call it white.

Stainless steel is used to make the cheapest fasteners. It has a number of advantages:

• does not rust (high - more than 10.5% - chromium content makes it resistant to corrosion);
• has a long service life - it is calculated in decades;
• strong enough to withstand heavy loads.

Conventional stainless steel screws are used for indoor work if the air humidity does not exceed 65%. Due to their not very attractive appearance, they are often hidden under plaster and other finishing materials.

Another type of white self-tapping screws is galvanized. They are made from carbon steel, so they have increased strength. However, due to the presence of carbon in the iron alloy, such fasteners quickly rust. To prevent corrosion from “eating” the metal, a layer of zinc is applied on top using the galvanic method.An additional advantage of galvanizing is that it gives the metal a noble silvery tint.

It is believed that galvanized self-tapping screws can be used both indoors and outdoors, but experienced craftsmen do not recommend using them to fasten parts that in the future will be exposed to frequent and prolonged exposure to moisture.

Yellow screws

There are two types of yellow self-tapping screws on sale, and most often galvanized fasteners have this shade. You were probably surprised, because a few lines above it was said that a layer of zinc applied to the metal ultimately gives a silver color. However, chemistry is not an easy science and sometimes allows you to create miracles. It is enough to treat silver self-tapping screws in a special passivating solution so that a yellow conversion film about 0.5 microns thick is formed on them. The composition of the mentioned solution includes salts of chromic acid, therefore this process of chemical “coloring” of the metal is called chromate passivation.

Passivation is carried out not only and not so much for the sake of achieving a decorative effect, but to increase anti-corrosion resistance. However, the beautiful color is the reason that yellow self-tapping screws are mostly used for finishing work, for example, for attaching door hinges and other parts visible to the eye.

More expensive fasteners are made from brass (a copper alloy that also includes iron, nickel, lead, manganese, and zinc). In comparison with their steel “brothers”, they win in several ways:

• have increased wear resistance;
• do not corrode even in the absence of protective coatings;
• have non-magnetic properties;
• remain reliable even under prolonged exposure to low temperatures.

Galvanized and brass yellow self-tapping screws are easy to distinguish - the former have a brighter, shiny, sometimes even rainbow color, while the latter look less attractive.

Black screws

Black self-tapping screws are one of the most popular. They are made of carbon steel, and the formation of a dark film on the surface is achieved in different ways.

Black galvanizing

The first method is the so-called black galvanizing. This is one of the types of chromatization. The thickness of the chromium layer can vary from 0.25 to 1 micron, providing, accordingly, varying degrees of corrosion protection.

When buying black screws, it is better to choose those that have been oiled - their resistance to rust is much higher. But in any case, fasteners coated with a layer of black galvanization are not intended for use in conditions of high humidity or in aggressive chemical environments.

Oxidation

The second method is oxidation. The oxide film formed on the surface of the metal is designed to protect it from corrosion, but copes with its task “C”. However, its anti-corrosion properties are slightly higher than those of black chrome film.

Oxidized screws can only be used indoors with low humidity levels.

For use in more severe conditions, the fasteners undergo additional processing:

• oiling;
• hydrophobization.

As a result, a coating is formed on the surface that repels water molecules. Most often, oxidized fasteners are purchased if there is a need to paint them in a specific color.

Phosphating

The third method is phosphating.The film with a thickness of 2–15 microns, formed on the metal as a result of this process, has the lowest decorative qualities, but provides good protective properties. This film consists of iron phosphates, and a powder called Majef salt (a mixture of manganese, iron and phosphorus) is used to apply it. The phosphate film is bonded to the surface of the screws at the molecular level, so it is almost impossible to damage it mechanically. In addition, paint adheres well to it.

Such fasteners are suitable for fastening materials at high humidity.

If you know that exposure to moisture will be prolonged, you should give preference to phosphated screws treated with hydrophobic substances.

Please note: there are also black self-tapping screws, the color of which is a result of simple painting and not anti-corrosion treatment. Check with the seller what metal they are made of and what qualities they have.

Now you can certainly buy exactly those self-tapping screws that are best suited for the task you have in mind. Choose the fasteners correctly, because the reliability, durability, and often safety of the structure depends on it.