Stainless Steel Fastener Knowledge Sharing

Stainless steel fasteners can withstand extreme temperature fluctuations, chemical corrosion, and mechanical pressure, while also offering an attractive appearance and long service life. These qualities make them the material of choice in marine engineering and food processing.

This article provides an in-depth analysis of the fundamentals of stainless steel fasteners, covering common standards, materials, markings, and their extensive applications across various industries. Whether you are an engineer, a procurement specialist, or a technical professional in related fields, this blog will offer a comprehensive understanding of stainless steel fasteners, empowering you to make more informed choices in practical applications.

What Are Stainless Steel Fasteners?

Stainless steel fasteners are mechanical components manufactured from stainless steel materials for connecting, fastening, and securing other parts. They are primarily used in environments requiring resistance to corrosion, high temperatures, oxidation, and chemical attack. Common stainless steel fasteners include bolts, nuts, screws, washers, and pins.

Common Fastener Standards

Hexagon Head Bolts

Name	Germany	Japan	USA	International	China
Full-thread external hex bolt	DIN 933	JIS B1180	ANSI/ASME B 18.2.1	ISO 4017	GB 5783, GB 30
Partial-thread hex head cap screw	DIN 931			ISO 4014	GB 5782
Round-head hex socket cap screw	DIN 912	JIS B 1176	ANSI/ASME B 18.3	ISO 4762	GB/T 70.1
Pan head socket head cap screw			ANSI/ASME B 18.3	ISO 7380	GB/T 70.2
Countersunk socket head cap screw	DIN 7991		ANSI/ASME B 18.3	ISO 10642	GB/T 70.3
Carriage bolt (round head square neck)	DIN 603	JIS B 1171	ANSI/ASME B 18.5	ISO 8677	GB 12
Pan head machine screw	DIN 7985	JIS B 1111	ANSI/ASME B 18.6.3	ISO 7045	GB 818
Countersunk machine screw	DIN 965			ISO 7046	GB 819
Pan head self-tapping screw	DIN 7981	JIS B 1122	ANSI/ASME B 18.6.4	ISO 7049	GB 845
Counterhead self-tapping screw	DIN 7982			ISO 7050	GB 846

Nuts

Name	Germany	Japan	USA	International	China
Hex nuts	DIN 934	JIS B 1181	ANSI/ASME B 18.2.2	ISO 4032	GB 6170
Hex thin nuts	DIN 439				GB 6172
Hex thick nuts					GB 6175
Hex nylon nuts	DIN 985		ASNI B 18.16.6	ISO 10511（thin）
Flange nuts	DIN 6923		IFI 145
Cap nuts	DIN 1587

Markings and Grades on Nuts and Bolts

Product markings on stainless steel fasteners are an important basis for verifying product quality and specifications. Correct markings allow users to determine the product’s material, strength, and intended use.

Stainless steel bolts are classified according to the type and performance grade of steel as follows: A1-50, A1-70, A1-80, A2-50, A2-70, A2-80, A3-50, A3-70, A3-80, A4-50, A4-70, A4-80, A5-50, A5-70, A5-80, C1-50, C1-70, C1-110, C4-50, C4-70, C3-80, F1-45, and F1-60. The first letter and number represent the stainless steel group, and the second and third numbers represent 1/10 of the tensile strength.

A2-70: “A2” indicates the material group, namely the second group A2 of austenitic steel. The material we commonly use is 304. “70” indicates the performance grade, with a minimum tensile strength of 700MPa.

A4-70: “A4” indicates the material group, namely the fourth group of austenitic steel, A4. The commonly used materials are 316 or 316L. “70” indicates the performance grade, with a minimum tensile strength of 700MPa.

A4-80: “A4” indicates the material group, namely the fourth group of austenitic steel, A4. The commonly used materials are 316 or 316L. “80” indicates that the minimum tensile strength is 800MPa or the load-bearing strength can reach 800MPa, which is equivalent to meeting the requirements of grade 8.8 carbon steel bolts or grade 8 carbon steel nuts.

The standard specifies the chemical composition of A2 and A4 stainless steel as follows:

Type	C	Si	Mn	P	S	Cr	Mo	Ni	Cu
A2	0.1	1	2	0.05	0.03	15-20	–	8-19	4
A4	0.08	1	2	0.045	0.03	16-18.5	2-3	10-15	4

Thread marking: such as “ISO 1500”, “UNF” indicates the standard and type of thread.

Manufacturer’s marking: Contains the manufacturer’s name or trademark, and the product source and quality can be traced.

Bolt Marking

Name	Material	Metric Standard Marking	Inch Standard Markings 3/4 or less	Inch Standard Markings 3/4 or more (included)	Unmarked Range	Type of Marking
Hexagon head bolts	304	A2-70 THE	F593C/THE	F593D/THE	M5 (1/4) and below (excluding)	Convex mark
	316	A4-70 THE	F593G316/THE	F593H316/THE
JIS		无	/			/
Hex socket（DIN 912, DIN 7991, ASME B18.3)	304	A2-70 THE	F837B/TONG			Concave marking
	316	A4-70 THE	F837E/TONG

Nut Marking

Name	Material	Metric Standard Marking	Inch Standard Markings 3/4 or less	Inch Standard Markings 3/4 or more (included)	Unmarked Range	Type of Marking
Standard nut DIN 934	304	A2-70 THE	F5944C/THE	F594D/THE	M5 (1/4) and below (excluding)	Concave marking
	316	A4-70 THE	F594G316/THE	F594H316/THE
Hex Heavy-Duty Nut	304	Standard heavy-duty nuts	F594C/THE	F594D/THE	/
		Solution-treated heavy-duty nuts.	8/THE	8A/THE
	316	Standard heavy-duty nuts	F594G316/THE	F594H316/THE
		Solution-treated heavy-duty nuts.	8M/THE	8MA/THE
Thin nuts	304	A2-035 THE	THE		/
	316	A4-040 THE	316/THE

How to Choose the Right Stainless Steel Material?

When selecting stainless steel hardware fasteners, the following factors need to be considered:

• Environmental conditions: For example, in marine or chemical environments, the A4 series or B8M series are recommended.
• Load requirements: Select an appropriate yield strength based on the load, such as A2-70, A2-80, A4-70, A4-80, etc.
• Standard requirements: Select materials that meet the relevant standards according to the specific application requirements, such as the F593 series.

A2 series stainless steel:

A2-304 is the basic 304 stainless steel, suitable for general industrial and civilian environments.

• A2-50 304: Yield strength of 500 MPa, suitable for medium load applications.
• A2-70 304: Yield strength of 700 MPa, suitable for higher load applications.
• A2-80 304: Yield strength up to 800 MPa, suitable for applications requiring high load and high strength.

A3 series stainless steel:

A3 series stainless steel offers superior corrosion resistance and toughness, making it suitable for harsher environments.

• A3: Basic A3 stainless steel, suitable for harsh environments.
• A3-50: Yield strength of 500 MPa, suitable for medium load applications.
• A3-70: Yield strength of 700 MPa, suitable for higher load applications.

A4 series stainless steel:

The A4 series, also known as 316 stainless steel, contains molybdenum, which further enhances its corrosion resistance, making it particularly suitable for marine and chemical environments.

• A4-50 316: Yield strength of 500 MPa for highly corrosive environments.
• A4-70 304/316: Yield strength of 700 MPa for high corrosion and higher load applications.
• A4-80 316: Yield strength of 800 MPa for very high loads and severe environments.

B8M series stainless steel:

B8M series stainless steel is an ASTM-compliant 316 stainless steel with excellent corrosion resistance for use in high-temperature and highly corrosive environments.

• B8M 316: Standard 316 stainless steel for extreme corrosive and high temperature environments.

F593 series stainless steel:

The F593 series of stainless steels are stainless steels that meet the ASTM F593 standard and are available in 304 and 316. This series is closely related to the American Standard and is suitable for applications requiring high strength and corrosion resistance.

• F593C 304: Standard 304 stainless steel with good corrosion resistance and mechanical properties.
• F593D 304: reinforced 304 stainless steel for higher strength applications.
• F593G 316: Standard 316 stainless steel for highly corrosive environments.
• F593H 316: Higher strength 316 stainless steel for extremely high corrosion and high strength requirements.

Differences between the ASTM F593 standard and other standards:

• ASTM F593: It is mainly used in the North American market, especially in the United States, and is widely used in the construction, machinery, petrochemical and other industries.
• Other standards: These standards are more common in Europe (DIN), the international market (ISO) and Japan (JIS), and the scope of application is relatively wide.

Material classification and naming:

• ASTM F593: Stainless steel fasteners are categorized into different grades, such as F593C, F593D, F593G, F593H, etc. Each grade corresponds to a specific type of stainless steel and performance requirements.
• Other standards (ISO/DIN/JIS): These standards usually use different naming and categorization. For example, the ISO standard uses A2, A4, etc. to indicate the type and grade of stainless steel, while the DIN standard uses a combination of numbers and letters (e.g. 1.4301 for 304 stainless steel).

Marking and certification:

• ASTM F593: requires fasteners to be clearly marked to identify their material and grade for easy identification and traceability. In addition, ASTM standards are often associated with specific certification and testing programs.
• Other standards: ISO, DIN, JIS and other standards have similar marking requirements, but the specific marking methods and certification procedures may vary.

If you have questions about your stainless steel hardware fastener options, contact our team at Beyond Fastener.

What Are the Benefits of Stainless Steel Fasteners?

1. Adaptability is more powerful, for stainless steel fasteners, to meet the requirements of the male thread size, then can be used, which can be seen in the stainless steel fasteners relative to the use of traditional anchor bolts for a wider range.
2. Installation is more simple, the previous traditional anchor bolt in the installation process is more complex, but today’s stainless steel fasteners in the installation process is relatively simple, this gives a lot of users to enhance the degree of convenience.
3. Problems encountered in the installation becomes less, do not need to go to the fear of traditional anchor bolt drilling will be tilted, through the stainless steel screw corrosion resistance and fracture cause analysis, in the installation of stainless steel screws can be directly punched holes, and then installed, so that the success rate can reach nearly one hundred percent.
4. The design is innovative, and this design ensures that the aesthetics of the stainless steel screws are greatly enhanced.
5. Can ensure that the stainless steel screws in the installation of a higher performance, to ensure that the degree of utilization of the screws has greatly improved.
6. Have good resistance to corrosion fatigue and wear corrosion performance, in some corrosive media conditions are used in pumps, valves and other equipment.

What are the uses of stainless steel nuts?

Stainless steel nuts are generally used in rust-resistant, high-temperature, electrically conductive and thermally conductive use environments, such as faucets, valves, and electrical switches. Another major use is injection, which is heated and embedded in plastic parts, or injected directly into a mold.

What Are the Disadvantages of Stainless Steel Fasteners?

Although the initial cost is higher and the life cycle cost is lower, it is the most economical component solution.

Not suitable for long-term preservation or long-term use, high production costs, rusting reaction in acidic solutions, easy to stick if not disassembled for a long time after locking.

Easy to slip or too much force is easy to break, toughness is worse than ordinary iron screws; can not replace 10.9, 12.9 and other high-strength screws.

Precautions for the Use of Stainless Steel Fasteners

Stainless steel fasteners can rust when not used properly. This will not only affect the level of aesthetics, but also affect the performance of stainless steel fasteners. So what should we pay attention to in the process of use?

  1、When storing stainless steel screws, ensure the environment remains dry. Galvanized iron screws should not be placed in damp locations. For non-standard parts with special requirements, use mesh bags or other packaging materials to wrap them, taking care to prevent mutual collision.

  2.Stainless steel screws must be handled with care during transportation to prevent damage caused by excessive shaking and friction between screws and fasteners. Fasteners should be arranged according to the instructions on the packaging boxes. Warehouse personnel should undergo unified training to guide operators through the actual transportation process and precautions for fasteners. This will prevent thread damage to screws, which could result in failure to pass go/no-go gauges and inability to install nuts.

  3.When using stainless steel screws or bolts, if nuts, washers, and other fasteners are required for assembly, it is essential to understand the performance characteristics of the mating components to ensure proper coordination.

  4.When using stainless steel products, ensure proper usage. For instance, torque should not exceed the minimum damage torque. The rust-proof coating on stainless steel screws must not be damaged during use. If the coating is damaged prior to use or requires removal, apply a rust-proof coating after assembly.

What Surface Finishes Are Available for Stainless Steel Fasteners?

Nowadays, most fastener manufacturers apply coatings to their products to enhance their visual appeal. However, stainless steel screws inherently possess superior properties and do not require surface coatings. Simply cleaning the outer layer of the stainless steel surface is sufficient. This process yields a smooth, lustrous finish. Below, BDfastener shares the cleaning methods and procedures for stainless steel screw surfaces to facilitate future maintenance and usage.

Degreasing

During the production process of stainless steel screws, they undergo numerous procedures, including exposure to machinery coated in machine oil. This explains why finished screws often retain oil stains on their surfaces, making thorough cleaning essential. Only through cleaning can stainless steel screws regain their true appearance. During cleaning, pour a degreasing liquid specifically designed for stainless steel into the solution. Clean at room temperature for 3 to 8 minutes, then rinse thoroughly with clean water and air-dry. This process yields a smooth stainless steel screw.

Polishing

Polishing is a common method for surface treatment of stainless steel screws. During the polishing process, machinery and abrasives are used to grind away burrs or protrusions on the screw surface. After a period of time, the surface of the stainless steel screw becomes noticeably brighter. Following another cleaning, the surface achieves an even higher level of brightness.

Remove oxide skin

Some fasteners develop oxide scale during production. To restore their shiny appearance, the surface oxide scale must be removed. The process follows the same steps as degreasing, but uses different cleaning agents. Specialized descaling agents are required. At room temperature, pour the cleaning agent into a mechanical agitation tank. Agitate and clean the stainless steel screws for 2 to 30 minutes, then rinse and filter the solution once more.

How to Buy Quality Stainless Steel Bolts and Nuts?

  一，Choose a reliable manufacturer

  When buying stainless steel fasteners, it is not the price of the fasteners that matters, but the manufacturer of these fasteners. For different manufacturers, they have different advantages in production, and the production technology and production process are also very different. Therefore, the quality of these fasteners will be very different, in order to make sure that the quality can meet our needs, then we should choose reliable manufacturers, because they have more advanced production technology, process and after-sales service, so as to ensure the quality of the screws!

  二，Purchase through official channels

  When buying stainless steel screws, many people prioritize low prices because they need to purchase in bulk. If the price is relatively low, they can save a lot of money. In this situation, they might choose to buy from lower-priced channels, but the quality of these products cannot be guaranteed. Therefore, we must choose regular prices. A better approach is to order directly from the manufacturer or a reputable distributor. Of course, you can also buy it through an e-commerce platform. After all, e-commerce platforms are vast and convenient. Therefore, it’s generally recommended to order directly from the screw manufacturer or from a reputable e-commerce platform. This way, if there are any problems, you can easily get replacements, saving you time and effort.

  三、Go to the official website of the relevant manufacturer to order

  To the relevant manufacturer’s official website for consultation and ordering, to buy good quality stainless steel fasteners, you can refer to the above two points to do. Or you can also combine and match with other methods, and when choosing a manufacturer, you can also make a site visit, so that they can have a clearer understanding of their production process and level of their own purchase is also assured.BDfastener is a reputable and credible manufacturer of fasteners, careful, careful, attentive; such as the purchase of stainless steel screws needs, welcome to contact BDfastener.

Related Resource Links

• ISO 3506：不锈钢紧固件标准
• DIN 931：六角螺栓标准