Summary of basic knowledge of fasteners

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1. Product name (standard)

Note: For screws that are not standard and are non-standard parts, drawings are required.

For example, DIN912, the Chinese name is: hexagon socket cylindrical head screw, this is the product name.

However, the most accurate approach is to call the standard, because GB70 is also such a name; however, there are many places where the two standards are not the same size.

The most influential standards in the world are: German standard (DIN), international standard (ISO), Chinese national standard (GB), American standard (ANSI), and Japanese standard (JIS).

2. Specifications

Generally, the name of the screw is the diameter of the tooth pattern and the length of the screw.

Tooth pattern diameter, metric system commonly used are: M2, M3, M4, M5, M6, M8, M10, M12, etc.;

Commonly used in the United States are:4#-40,6#-32,8#-32,10#-24,1/4-20,5/16-18,3/8-16,1/2- 13 and so on.

The length of the screw refers to the effective length of the embedded object.For example: countersunk head screws are loaded with the total length, semi-countersunk head screws must add half the length of the head, while the length of cylindrical head screws does not include the head size.such as:

For specifications, it is best to add pitch to the full name.For example, M4-0.7x8, 4 refers to the outer diameter of the tooth is 4mm, 0.7 refers to the distance between the two tooth peaks is 0.7mm, and 8 refers to the effective length of the embedded object is 8mm.

In order to simplify and not write the pitch, we default the thick teeth to the standard teeth, because they are the most common; this way there is no need to mark them.This is only available in the metric system, and U.S.-made products still have to be marked with pitch.

Here we will focus on the specifications of American-made screws. For example, 6#-32*3/8, 6# is the outer diameter of the tooth, which is close to 3.5mm; 32 is the thread length of each inch with 32 teeth (equivalent to the pitch of metric screws); 3/8 is the length of the screw (the specific metric screw).

There are two formulas to remember here: tooth outer diameter A#= (Ax0.013+0.06) x25.4 (mm), 1 inch=25.4mm.

Among them, 2#=2.2mm, 4#=2.9mm, 6#=3.5mm, 8#4.2mm, and 10#=4.8mm are the data that must be memorized.The number of teeth corresponding to the screws of each specification must also be memorized:2#-56,4#-40,6#-32,8#-32,10#-24,1/4-20,5/16-18,3/8-16,1/2-13( American-made standard teeth).

Note: American-made UNC teeth are standard teeth, and UNF is fine teeth.We default coarse teeth to standard teeth.

3. Material

The most common materials are: carbon steel, stainless steel, stainless iron, copper, aluminum, etc.

Carbon steel is divided into low-carbon steel (such as C1008/C1010/C1015/C1018/C1022), medium-carbon steel (such as C1035), high-carbon steel (C1045/C1050), and alloy steel (SCM435/10B21/40Cr).

Generally, C1008 materials are made of ordinary grade products, such as 4.8 grade screws and ordinary grade nuts; C1015 is generally made of ring screws; C1018 is generally made of machine screws, of course, it is also used for self-tapping nails; C1022 is generally used for self-tapping nails; C1035 is made of 8.8 grade screws; C1045/10B21/40Cr is made of 10.9 grade screws; 40Cr/SCM435 is made of 12.9 grade screws.

Stainless steel has SS302/SS304/SS316 as the most common.Of course, a large number of SS201 products are also popular now, and even products with lower nickel content are called non-authentic stainless steel products; the appearance looks similar to stainless steel, but the anticorrosive properties are much different.

4. Strength level

The strength grade mainly refers to carbon steel fasteners.

The common strength grades of carbon steel screws are: Grade 4.8, grade 5.8, grade 6.8, grade 8.8, grade 10.9, and grade 12.9.The nuts are correspondingly: level 4, level 6, level 8, level 10, and level 12.

Generally, screws below grade 8.8 are called ordinary screws, while screws above grade 8.8 (including grade 8.8) are high-strength screws.The difference is that high-strength screws need to be tempered and heat treated.

5. Surface treatment

The surface treatment is mainly to increase the anticorrosive properties, and some parts also take into account the color, so it is mainly for carbon steel products, which generally need to be surface treated.

Common surface treatments are: blackening, galvanized, copper-plated, nickel-plated, chrome-plated, silver-plated, gold-plated, dacromet, hot-dip zinc, etc.;

There are many types of galvanized, including blue and white zinc, blue zinc, white zinc, yellow zinc, black zinc, green zinc, etc. At the same time, it is also divided into environmentally friendly and non-environmentally friendly. Each type of plating has a variety of coating thicknesses to meet different salt spray test effects.