6 Basics You Should Know About Fasteners

The parameters to be indicated for describing fasteners include: product name (standard), specification, material, strength grade and surface treatment.

Such as DIN912, M4-0.7×8, SCM435, grade 12.9, blackening.

1. Product name (standard)

Note: if there is no standard screw and it belongs to non-standard parts, drawings need to be provided.

For example, DIN912, the Chinese name is Hexagon socket cylindrical head screw, which is the product name.

However, the most accurate way is still to call the standard, because GB70 is also such a product name;

However, there are many inconsistencies between the two standards.

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. Fastener Specifications

Generally, the designation of screw is tooth pattern diameter -screw length.

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

Commonly used in American system: 4 #-40, 6 #-32, 8 #-32, 10 #-24, 1 / 4-20, 5 / 16-18, 3 / 8-16, 1 / 2-13, etc.

The screw length refers to the effective length embedded in the loaded object.

For example: countersunk head screws are loaded with the total length, half countersunk head screws need to add the length of half head, while the length of cylindrical head screws does not include the head size. For example:

For the specification, the full name is better to add the pitch.

For example, M4-0.7×8, 4 refers to the tooth outer diameter of 4mm, 0.7 refers to the distance between two tooth peaks of 0.7mm, and 8 refers to the effective length of embedded object of 8mm.

In order to simplify and not write the pitch, we default the coarse teeth to the standard teeth, because it is the most common;

So you don’t have to mark it.

This point is only available in metric system. American products still need standard tooth pitch.

Here we focus on the specifications of American screws.

For example, 6#-32 * 3 / 8, 6# is the outer diameter of the tooth, which is close to 3.5mm;

32 is 32 teeth per inch of thread length (equivalent to the pitch of metric screws);

3 / 8 is the length of the screw (specifically the same as metric screw).

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 to be memorized.

The number of teeth corresponding to each specification of screw must also be remembered: 2#-56, 4#-40, 6#-32, 8#-32, 10#-24, 1 / 4-20, 5 / 16-18, 3 / 8-16, 1 / 2-13 (American Standard teeth).

Note: US made UNC teeth are standard teeth and UNF are fine teeth. We default coarse teeth to standard teeth.

3. Fastener Material

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

Carbon steel is also 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 is made of ordinary grade products, such as grade 4.8 screws and ordinary grade nuts;

C1015 generally use lifting eye screws;

C1018 is generally used to make machine screws.

Of course, it is also used to make self tapping screws;

C1022 is generally used as self tapping screw;

C1035 make grade 8.8 screws;

C1045 / 10B21 / 40Cr screw with grade 10.9;

40Cr / SCM435 make grade 12.9 screws.

Stainless steel has SS302 / SS304 / SS316 as the most common.

Of course, a large number of SS201 products are popular now, even products with lower nickel content.

We call them non authentic stainless steel products;

The appearance looks similar to that of stainless steel, but the anti-corrosion performance is very different.

4. Fastener strength grade

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.

Nuts are: Grade 4, grade 6, Grade 8, grade 10 and grade 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 undergo quenching and tempering heat treatment.

5. Fastener surface treatment

The surface treatment is mainly to increase the anti-corrosion performance, and some give consideration to the color, so it is mainly for carbon steel products, which generally need surface treatment.

Common surface treatments include blackening, galvanizing, copper plating, nickel plating, chromium plating, silver plating, gold plating, Dacromet, hot dip galvanizing, etc;

There are many kinds of zinc plating, 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 environmental protection and non environmental protection.

Each plating has a variety of coating thickness to meet different salt spray test results.


Fasteners usually include the following 13 types

1. Bolt

A kind of fastener composed of head and screw (cylinder with external thread), which needs to be matched with nut to fasten and connect two parts with through holes.

This type of connection is called bolt connection.

If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a removable connection.

2. Studs

There is no head, only a kind of fastener with external threads on both ends.

When connecting, one end of it must be screwed into the part with internal thread hole, and the other end must pass through the part with through hole, and then screw on the nut, even if the two parts are firmly connected as a whole.

This connection form is called stud connection, which is also a detachable connection.

It is mainly used when one of the connected parts is thick, requires compact structure, or is not suitable for bolt connection due to frequent disassembly.

3. Screw

It is also a kind of fastener composed of head and screw.

It can be divided into three categories according to purpose: machine screw, set screw and special purpose screw.

Machine screws are mainly used for the fastening connection between a part with a fixed threaded hole and a part with a through hole, without nut matching (this connection form is called screw connection, which also belongs to removable connection; it can also be matched with nuts, which is used for the fastening connection between two parts with a through hole.) The set screw is mainly used to fix the relative position between two parts.

Special purpose screws, such as eyebolt, are used for hoisting parts.

4. Nut

With internal thread hole, the shape is generally flat hexagonal column, or flat square column or flat cylindrical.

It is used to fasten and connect two parts into a whole with bolts, studs or machine screws.

5. Self tapping screw

Similar to machine screws, but the thread on the screw is a special thread for self tapping screws.

It is used to fasten and connect two thin metal components into a whole.

Small holes need to be made on the component in advance.

Because the screw has high hardness, it can be directly screwed into the hole of the component to form a responsive internal thread in the component.

6. Wood screw

It is also similar to the machine screw, but the thread on the screw is a special thread for wood screw, which can be directly screwed into the wooden component (or part) to firmly connect a metal (or non-metal) part with a through hole with a wooden component.

This connection is also a detachable connection.

7. Washer

A kind of fastener with flat circular shape.

It is placed between the support surface of bolts, screws or nuts and the surface of connecting parts to increase the contact surface area of connected parts, reduce the pressure per unit area and protect the surface of connected parts from damage;

Another kind of elastic washer can also prevent the nut from loosening.

8. Retaining ring

It is installed in the shaft groove or hole groove of the machine and equipment and plays the role of preventing the parts on the shaft or hole from moving left and right.

9. Pin

It is mainly used for positioning parts, and some can also be used for connecting parts, fixing parts, transmitting power or locking other fasteners.

10. Rivets

A kind of fastener composed of head and nail rod, which is used to fasten and connect two parts (or components) with through holes to make them a whole.

This connection form is called rivet connection, which is called riveting for short.

It is connected with non detachable.

Because to separate the two parts connected together, the rivets on the parts must be destroyed.

11. Assembly and connecting pair

Assembly refers to a kind of fastener supplied in combination, such as the combination of a certain machine screw (or bolt, self supplied screw) and flat washer (or spring washer, lock washer);

Connecting pair refers to a kind of fastener that combines a special bolt, nut and washer.

12. Welding nail

As a heterogeneous fastener composed of light energy and nail head (or no nail head), it is fixedly connected to one part (or component) by welding, so as to connect with other parts.

13. Steel wire screw sleeve

Steel wire screw sleeve is a new type of threaded connection element, which is refined from high-strength and high-precision corrosion-resistant rhombic wire.

Shaped like a spring, it is installed in a specific screw hole of the matrix, and its inner surface forms a standard thread.

When matched with the screw (bolt), it can significantly improve the strength and wear resistance of threaded connection;

Especially in low strength materials such as aluminum, magnesium, cast iron and plastics.

Locking type is to add one or several circles of locking ring on the basis of ordinary type.

Xinxiang Yongda Industrial Co., Ltd. is a manufacturer specializing in the production of steel wire screw sleeves. It is suggested that steel wire screw sleeves should be embedded into the threads of low-strength engineering materials such as aluminum, magnesium alloy, cast iron, FRP and plastics to form standard m and MJ threads, which have the functions of continuous strength, impact resistance and wear resistance, disperse stress, protect the threads of the matrix and greatly prolong the service life of the matrix.

At the same time, the stress condition of the thread is improved, the elastic connection is formed, the pitch and half angle error between the internal and external threads are eliminated, the load on the thread is evenly distributed, the base thread is protected from damage and the service life is prolonged.

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