6 Must-Know Basics About Fasteners

Are you tired of struggling to understand the different types of fasteners and their specifications? Do you feel overwhelmed by the vast variety of screws, bolts, and nuts available in the market? Look no further!

Our comprehensive guide to fasteners covers everything you need to know about their product names, specifications, materials, strength grades, and surface treatments. From metric to American standards, we’ve got you covered.

So, sit back, relax, and let us guide you through the basics of fasteners.

The parameters used to describe fasteners should include the product name (standard), specification, material, strength grade, and surface treatment. For example, DIN912, M4-0.7×8, SCM435, grade 12.9, and blackening.

1. Product name (standard)

Note: If a screw is non-standard and does not belong to a standard part, drawings must be provided.

For instance, DIN912, known in Chinese as Hexagon Socket Cylindrical Head Screw, is the product name. Nonetheless, the most precise way is still to refer to the standard, such as GB70, which is also a product name.

However, there are several 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

In general, the designation of a screw includes the tooth pattern diameter followed by the screw length.

The tooth pattern diameter is usually expressed in metric units, with common sizes including M2, M3, M4, M5, M6, M8, M10, M12, and so on.

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 length of a screw refers to the effective length that is embedded in the loaded object.

For example, countersunk head screws are loaded with their total length, while half countersunk head screws require the length of half of the head to be added. On the other hand, the length of cylindrical head screws does not include the size of the head. For instance:

When specifying the screw, it’s better to include the pitch in the full name. For instance, M4-0.7×8, where 4 represents the outer diameter of the tooth, 0.7 refers to the distance between two tooth peaks of 0.7mm, and 8 represents the effective length of the embedded object of 8mm.

To simplify things and avoid writing the pitch, we default to coarse teeth as the standard teeth since they are the most common. Therefore, there is no need to mark it.

This information is only available in the metric system. American products still require standard tooth pitch.

Here, we will focus on the specifications of American screws.

For instance, 6#-32 * 3/8, where 6# is the outer diameter of the screw, which is approximately 3.5mm;

32 refers to the number of 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).

There are two formulas to remember here: tooth outer diameter a#= (ax0.013 + 0.06) X25.4 (mm), and 1 inch = 25.4mm.

Among them, the data to be memorized are: 2#=2.2mm, 4#=2.9mm, 6#=3.5mm, 8#=4.2mm, and 10#=4.8mm.

Furthermore, the number of teeth corresponding to each specification of the screw must 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: UNC teeth made in the US are standard teeth, while UNF are fine teeth. We default coarse teeth to standard teeth.

3. Fastener Material

The most commonly used materials are carbon steel, stainless steel, stainless iron, copper, and aluminum.

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

Grade 4.8 screws and ordinary grade nuts are typically made of C1008, which is an ordinary grade product.

Lifting eye screws are usually made of C1015, while machine screws are made of C1018. Additionally, C1018 is also used to make self-tapping screws.

C1022 is typically used as a self-tapping screw, and C1035 is used to make grade 8.8 screws. C1045/10B21/40Cr screws are made with grade 10.9, while grade 12.9 screws are made with 40Cr/SCM435.

The most commonly used types of stainless steel are SS302/SS304/SS316. However, many products now use SS201, which has a lower nickel content. These are known as non-authentic stainless steel products. While their appearance may look similar to stainless steel, their anti-corrosion performance is significantly different.

4. Fastener strength grade

The term strength grade primarily pertains to carbon steel fasteners.

The common strength grades for carbon steel screws include grade 4.8, grade 5.8, grade 6.8, grade 8.8, grade 10.9, and grade 12.9.

As for nuts, they are categorized as Grade 4, grade 6, grade 8, grade 10, and grade 12.

Usually, screws with a grade below 8.8 are known as ordinary screws, whereas screws with a grade of 8.8 or higher (including grade 8.8) are high-strength screws.

The distinction between the two is that high-strength screws require quenching and tempering heat treatment.

5. Fastener surface treatment

Surface treatment is primarily used to improve anti-corrosion performance, with some attention paid to color. Therefore, it is mainly applied to carbon steel products, which generally require surface treatment.

Common surface treatments include blackening, galvanizing, copper plating, nickel plating, chromium plating, silver plating, gold plating, Dacromet, hot dip galvanizing, among others.

Zinc plating, for instance, comes in various forms such as blue and white zinc, blue zinc, white zinc, yellow zinc, black zinc, green zinc, among others, and can be categorized as environmental and non-environmental.

Each plating has multiple coating thickness options to meet diverse salt spray test requirements.


Fasteners usually include the following 13 types

1. Bolt

A fastener is a type of hardware used to connect two parts that have through holes. It typically consists of a head and a screw, which is a cylinder with external threading. In order to fasten the parts together, a nut is needed to be paired with the screw, creating what is known as a bolt connection.

The bolt connection is considered a removable connection since the two parts can be separated by unscrewing the nut from the bolt.

2. Studs

There is no head; instead, it has a kind of fastener with external threads on both ends.

When connecting, one end of the fastener must be screwed into the part with an internal threaded hole, while the other end must pass through the part with a through hole. After that, the nut can be screwed on, which will result in both parts being firmly connected as a whole.

This type of connection is called a stud connection, which is also a detachable connection.

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

3. Screw

A fastener composed of a head and a screw, can be classified into three categories based on its purpose: machine screws, set screws, and special-purpose screws.

Machine screws are primarily used for fastening connections between a part with a fixed threaded hole and a part with a through hole, without the need for a matching nut (this connection form is called screw connection and is also a type of removable connection). It can also be matched with nuts for fastening connections between two parts with a through hole.

Set screws are mainly used to fix the relative position between two parts.

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

4. Nut

The shape of an internal thread hole is generally a flat hexagonal column, flat square column, or flat cylindrical shape.

These holes are used to fasten and connect two parts together with bolts, studs, or machine screws.

5. Self tapping screw

Self-tapping screws have a special thread that distinguishes them from machine screws. They are designed to fasten and connect two thin metal components together.

To use self-tapping screws, small holes must be created in the components beforehand. As these screws are highly durable, they can be inserted directly into the holes to create an internal thread within the component.

6. Wood screw

The wood screw is similar to a machine screw, but it has a unique thread designed specifically for use with wood. This thread allows the screw to be easily and securely screwed directly into a wooden component, connecting it to a metal or non-metal part with a through hole.

This connection is also detachable, meaning that it can be easily undone when necessary.

7. Washer

A fastener with a flat circular shape is known as a washer. It is used between the support surface of bolts, screws, or nuts and the surface of connecting parts to increase the contact surface area of the connected parts. This, in turn, helps to reduce the pressure per unit area and protect the surface of the connected parts from damage.

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

8. Retaining ring

It is installed in the groove of a shaft or hole in machinery and equipment, and its purpose is to prevent the components on the shaft or hole from moving laterally.

9. Pin

It is mainly used to position parts, and some can also serve for connecting parts, fixing components, transmitting power, or securing other fasteners.

10. Rivets

A fastener made up of a head and a nail rod is used to connect two parts or components with through holes, creating a single, unified structure. This connection is referred to as a rivet connection or simply riveting, and it is non-detachable. To separate the two parts joined by rivets, the rivets themselves must be destroyed.

11. Assembly and connecting pair

Assembly refers to a type of fastener supplied as a combination of certain machine screws (or bolts, self-supplied screws) and flat washers (or spring washers, lock washers).

A connecting pair refers to a type of fastener that combines a special bolt, nut, and washer.

12. Welding nail

A fastener is a heterogeneous component made up of light energy and a nail head (which may or may not be present). It is used to create a fixed connection between one part or component and other parts by means of welding.

13. Steel wire screw sleeve

The steel wire screw sleeve is a newly developed threaded connection element made from high-strength and high-precision corrosion-resistant rhombic wire.

Resembling a spring, it is designed to fit into a specific screw hole in the matrix, and its inner surface creates a standard thread. When paired with a screw (bolt), it significantly enhances the strength and wear resistance of the threaded connection, particularly in low-strength materials such as aluminum, magnesium, cast iron, and plastics.

The locking type of the steel wire screw sleeve includes one or more circles of locking rings added to the ordinary type.

Xinxiang Yongda Industrial Co., Ltd. is a manufacturer specializing in the production of steel wire screw sleeves. We recommend that steel wire screw sleeves be embedded into the threads of low-strength engineering materials such as aluminum, magnesium alloy, cast iron, FRP, and plastics to create standard m and MJ threads, which offer continuous strength, impact resistance, and wear resistance. They disperse stress, protect the threads of the matrix, and significantly extend the matrix’s service life.

Moreover, the stress condition of the thread is improved, an elastic connection is formed, and 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 safeguarded against damage, and the service life is prolonged.

Professional Insights

Get Expert Advice on Metalworking Machines

Let our experts help you choose the right metalworking machine for your needs.

About The Author

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top