In order to facilitate use, management and description, certain methods need to be adopted to classify them. The standard parts center has summarized several common methods for classifying fasteners:
Methods for classifying fasteners
1. By application field
According to the different application fields of fasteners, internationally, fasteners are divided into two categories: one is general-purpose fasteners, and the other is aerospace fasteners.
General-purpose fasteners are the commonly used ordinary fasteners. The standards of these fasteners are formulated and overseen by ISO/TC2 (International Organization for Standardization/Standardization Technical Committee for Fasteners) internationally, and national standards or standardization association standards appear in various countries. The national fastener standards in China are formulated and overseen by the National Fastener Standardization Technical Committee (SAC/TC85).
These fasteners adopt the common thread and mechanical performance grade system, and are widely used in machinery, electronics, transportation, stores, construction, chemical industry, ships, and other fields, and can also be used for aerospace ground products and electronic products.
The mechanical performance grade system can reflect the comprehensive mechanical performance of fasteners, but mainly reflects the bearing capacity. This system generally limits the material category and composition, but does not limit the specific material brand. The standard parts center provides you with
Aerospace fasteners are fasteners specially designed for aerospace aircraft. The standards of these fasteners are formulated and overseen by ISO/TC20/SC4 (International Organization for Standardization/Aerospace Standardization Technical Committee/Aerospace Fastener Technical Committee).
The aerospace fastener standards in China are composed of national military standard fasteners, aviation standards, and aerospace standards. The main characteristics of aerospace fasteners are as follows: The standard parts center provides you with
(1) The thread adopts MJ thread (metric), UNJ thread (imperial) or MR thread.
(2) Strength classification and temperature classification are adopted.
(3) High strength, light weight, with strength grades generally above 900 Mpa, up to 1800 MPa or even higher.
(4) High precision, good anti-loosening performance, high reliability.
(5) Can adapt to complex environments.
(6) There are strict requirements for the used materials, etc.
2. Classification according to traditional practices
According to traditional practices in our country, fasteners are classified into 13 major categories: bolts, studs, nuts, screws, wood screws, self-tapping screws, washers, rivets, pins, retaining rings, connection pairs and fastener-combination components, and others. This classification method has been consistently used in our country’s national standards.
3. By whether standards have been formulated
According to whether standards have been formulated, fasteners are classified as standard fasteners and non-standard fasteners. Standard fasteners refer to fasteners that have been standardized and formed standards, such as national standard fasteners, military standard fasteners, aviation standard fasteners, aerospace standard fasteners and enterprise standard fasteners, etc. Non-standard fasteners refer to fasteners that have not formed standards.
With the expansion of application scope, the trend of non-standard fasteners will gradually form standards and transform into standard fasteners; some non-standard fasteners, due to various complex factors, can only continue to be used as special parts. The standard parts center provides you with
4. By whether the geometric structure contains thread features
Fasteners are classified as threaded fasteners (such as bolts, nuts, etc.) and non-threaded fasteners (such as washers, retaining rings, pins, ordinary rivets, ring-slot rivets, etc.) according to whether the geometric structure contains thread features.
Threaded fasteners are fasteners that achieve connection through threads. Threaded fasteners can be further subdivided.
According to the different types of threads, threaded fasteners are divided into metric threaded fasteners, unified imperial threaded fasteners, etc.
According to the characteristics of the formed body, threaded fasteners are divided into external threaded fasteners (such as bolts, studs), internal threaded fasteners (such as nuts, self-locking nuts, high-lock nuts) and external and internal threaded fasteners (such as threaded bushings) 3 categories. Based on the position characteristics of the threads on the fasteners, external threaded fasteners are classified into screws, bolts and studs.
5. Classification by material
According to the different materials used, fasteners are classified as carbon structural steel fasteners, alloy structural steel fasteners, stainless steel fasteners, high-temperature alloy fasteners, aluminum alloy fasteners, titanium alloy fasteners, titanium-nickel alloy fasteners and non-metal fasteners, etc.
6. Classification by main forming process methods
According to the different forming process methods, fasteners can be classified as upsetting fasteners (such as aluminum alloy rivets), cutting fasteners (such as screws and nuts processed from hexagonal bar materials) and upsetting-cutting core-type fasteners (such as most screws, bolts and high-lock bolts). Upsetting also includes cold upsetting and hot (warm) upsetting.
7. Classification by final surface treatment status
According to the differences in final surface treatment status, fasteners are classified as untreated fasteners and treated fasteners. Untreated fasteners generally do not undergo special treatment. After the processing and heat treatment procedures are qualified, necessary cleaning is carried out before storage and shipment.
Treated fasteners, the types of surface treatment are detailed in the chapter of fastener surface treatment. Fasteners treated with galvanization are called galvanized fasteners, those treated with cadmium plating are called cadmium-plated fasteners, and those treated with oxidation are called oxidized fasteners. And so on.
8. Classification by strength
According to the difference in strength level, fasteners are classified into low-strength fasteners, medium-high strength fasteners, high-strength fasteners and ultra-high strength fasteners. The fastener industry conventionally refers to fasteners with a mechanical performance grade lower than 8.8 or a nominal tensile strength lower than 800 MPa as low-strength fasteners.
Fasteners with a mechanical performance grade between 8.8 and 12.9 or a nominal tensile strength between 800 MPa and 1200 MPa are called medium-high strength fasteners. Fasteners with a nominal tensile strength between 1200 MPa and 1500 MPa are called high-strength fasteners, and fasteners with a nominal tensile strength higher than 1500 MPa are called ultra-high strength fasteners.
9. Classification by nature of working load
According to the differences in the nature of working load, fasteners are classified into tensile type and shear type. Tensile type fasteners mainly bear tensile load or tensile-combined shear load; shear type fasteners mainly bear shear load. There are certain differences in nominal rod diameter tolerance and thread length of threaded fasteners between tensile type and shear type fasteners.
10. Classification by requirements of assembly operation
According to the differences in assembly operation requirements, fasteners are classified as single-side connection fasteners (also known as blind connection fasteners) and double-side connection fasteners. Single-side connection fasteners only need to operate on one side of the connected component to complete the assembly, such as screws, ejecting rivets, etc.; double-side connection fasteners must operate on both sides of the connected component to complete the assembly, such as bolts – nuts pairs, ordinary rivets, etc.
11. Classification by whether they can be disassembled after assembly
According to whether they can be disassembled after assembly, fasteners are classified as detachable fasteners and non-detachable fasteners. Detachable fasteners refer to fasteners that need to be disassembled during use and can be disassembled, such as bolts, screws, ordinary nuts, washers, etc.
Non-detachable fasteners refer to fasteners that do not undergo disassembly with the connected component during use; when disassembly is necessary, these fasteners can also be disassembled, but it often leads to damage to the fastener or the link system and cannot be reused. Such fasteners include various rivets, high-lock bolts, studs, high-lock nuts, etc.
12. Classification by technical content
According to the differences in technical content, fasteners are classified into low-end, mid-end and high-end three levels. In the fastener industry, general-purpose fasteners with a maximum marking accuracy of no more than level 7 and a strength of less than 800 MPa are commonly referred to as low-end fasteners. These fasteners have relatively low technical difficulty, low technical content and low added value.
Fasteners with a maximum marking accuracy of level 6 or 5, a strength ranging from 800 MPa to 1200 MPa, and certain material requirements are classified as mid-range fasteners. These fasteners have certain technical difficulty, certain technical content and relatively high added value.
Special material fasteners with a marking accuracy exceeding level 5, a strength exceeding 1200 MPa, or with requirements for anti-fatigue, anti-high-temperature creep, or special anti-corrosion and lubrication are classified as high-end fasteners.
These fasteners have high technical difficulty, high technical content and high added value. There are many other classification methods for fasteners, such as classifying them based on the head structure of the fasteners, and so on. They will not be listed one by one. As materials, complete equipment systems and process means continue to be innovated, people will propose new classification methods for fasteners according to their needs.
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