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What is the difference between screws, bolts, and nuts?

Jul 07,2025

Flange nuts: mainly used to increase the contact surface with workpieces, mostly in pipelines, fasteners, and some stamped and cast parts.

(1) Bolt:

A type of fastener consisting of a head and a screw (cylindrical body with external threads) that needs to be matched with a nut to securely 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 bolt connection is a detachable connection.

(2) Screw:

A type of fastener consisting of a head and a screw, which can be divided into three categories according to their use - machine screws, set screws, and special-purpose screws. Machine screws are mainly used for fastening connections between a part with an internal threaded hole and a part with a through-hole, without the need for nut fitting (this type of connection is called a screw connection, which is also a detachable connection; it can also be used in conjunction with a nut for fastening connections between two parts with through-hole). Set screws are mainly used to fix the relative position between two parts. Special purpose screws include lifting ring screws, which are used for lifting parts.

The best material is 316 corrosion-resistant stainless steel, followed by 304. Next is carbon steel, which is also the most commonly used material.

What are the standards and uses of hex nuts? As a standard component, nuts and rivets have their own standards. The editor summarizes the standards for hexagonal nuts for differentiation, connection, and their purposes.

For hex nuts, commonly used standards include:

GB41 Type I Hexagonal Nut - Grade C

GB6170 Type I Hexagonal Nut - Grade A and B

GB6171 Type I Hexagonal Nut - Fine Thread - Grades A and B

GB6172 Hexagonal Thin Nut - Grades A and B - Chamfering

GB6173 Hexagonal Thin Nut - Fine Thread - Grades A and B

GB6174 Hexagonal Thin Nut - Grade B - No Chamfering

GB6175 Type II Hexagon Nut - Grade A and B

GB6176 Type II Hexagonal Nut - Fine Thread - Grade A and B

GB6177 Hexagonal Flange Nut - Grade A

GB55 hexagonal thick nut

GB56 hexagonal thick nut

GB1229 Large Hexagon Nut (High Strength for Steel Structures)

1. Ordinary hex nut:

It has a wide range of applications and is characterized by strong fastening force. However, the disadvantage is that there needs to be sufficient operating space during installation. During installation, adjustable wrenches, open-end wrenches, or eyeglass wrenches can be used, all of which require a large operating space.

2. Cylindrical head hexagon nut:

It is the most widely used screw among all screws because it has a relatively high tightening force and can be operated with an internal hex wrench. It is easy to install and can be used in almost various structures. Its appearance is relatively beautiful and neat. The disadvantage is that the tightening force is slightly lower than that of the external hex, and repeated use can easily damage the internal hex and make it impossible to disassemble.

3. Pan head hexagon nut:

It is rarely used in machinery and has the same mechanical properties as before. It is mostly used in furniture to increase the contact surface with wooden materials and enhance the aesthetic appearance.

4. Headless hex nut:

It is necessary to use certain structures, such as top wire structures that require a large amount of tightening force, or places where the cylindrical head needs to be hidden.

5. Countersunk hexagonal nut:

Mostly used in power machinery, its main function is the same as that of an internal hexagon.

6. Nylon locking nut:

A structure with nylon rubber rings embedded in the hexagonal surface to prevent loose threads, used on powerful machinery.

7. Flange nuts: mainly used to increase the contact surface with workpieces, mostly in pipelines, fasteners, and some stamped and cast parts.

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