We often see numbers like 4.8, 8.8 marked on fastener products. What do these mean? Actually, these are strength standards from the European EN ISO 898-1. For example, in the case of 8.8, the first 8 represents the maximum tensile strength of the product, which is 800 MPa. The second 8 represents the maximum yield strength, which is 0.8 times 800 MPa, or 640 MPa.
|
Parameter |
Ultimate Tensile Strength (UTS) |
Yield Strength |
|
Definition |
Maximum tensile stress |
Maximum elastic limit stress |
|
Unit |
MPa |
MPa |
Tensile strength and yield strength are important parameters for evaluating the mechanical properties of fasteners.
Ultimate Tensile Strength (UTS) is the maximum tensile stress that a material can withstand. If this stress is exceeded, the material will fracture. UTS is one of the most important indicators for fasteners because it reflects the material's maximum load-bearing capacity under tensile load.
Yield strength is the maximum stress that a material can withstand before it undergoes permanent deformation. Beyond this stress, the material will experience plastic deformation, meaning it will not return to its original shape even after the load is removed. Yield strength is a crucial parameter for determining whether a material is suitable for use as a fastener.
The Ultimate Tensile Strength (UTS) is usually greater than the yield strength. For example, a grade 8.8 bolt has a tensile strength of 800 MPa and a yield strength of 640 MPa (800 × 0.8).
The common strength grades of carbon steel fasteners include 4.8, 5.8, 6.8, 8.8, 10.9, and 12.9. Among these, screws with a strength grade below 8.8 are referred to as regular screws, while those with a strength grade of 8.8 and above are referred to as high-strength screws. The most common grades are 4.8, 6.8, and 8.8, which are predominantly used in Meigesi's fasteners.
In the United States, the standards used are ASTM, with common strength grades including grades 2, 5, 8, 9, and 12. Grade 2 in ASTM is equivalent to grade 4.8 in EN ISO 898-1.
The strength specifications for nuts differ from the aforementioned standards. The performance grades for nuts are relatively simple and are divided into two categories: thin nuts and standard nuts. Thin nuts represent a reduced load-bearing capacity, and their performance grades are 04 and 05. The leading "0" indicates that the product has reduced load-bearing capacity, while the subsequent "4" and "5" denote guaranteed stress divided by 100.
The performance grades for standard nuts include grades 5, 6, 8, 9, 10, and 12. This indicates that when selecting a matching bolt, the first digit of the bolt's performance grade should not exceed the grade of the nut. For example, with an 8-grade nut, the matching bolt should not exceed a performance grade of 8.8. The main reason for this is economic efficiency, as the strength of the nut does not need to be higher than that of the bolt. However, if higher strength for the nut is required, a 10-grade nut can be paired with an 8.8-grade bolt.
|
Identification Grade Mark |
Specification /Grade |
Material |
Nominal Size Range (in.) |
Mechanical Properties | ||
|---|---|---|---|---|---|---|
|
Proof Load (psi) |
Yield Strength Min(psi) |
Tensile Strength Min(psi) | ||||
 No Grade Mark |
SAE J429 Grade 1 |
Low or Medium Carbon Steel |
1/4 thru 1-1/2 | 33,000 | 36,000 | 60,000 |
|
ASTM A307 Grades A&B |
Low Carbon Steel |
1/4 thru 4 | -- | -- | ||
|
SAE J429 Grade 2 |
Low or Medium Carbon Steel |
1/4 thru 3/4 Over 3/4 to 1-1/2 |
55000 | 57000 |
74,000 60,000 |
|
| 33,000 | 36,000 | |||||
|
No Grade Mark |
SAE J429 Grade 4 |
Medium Carbon Cold Drawn Steel |
1/4 thru 1-1/2 | -- | 100,000 | 115,000 |
|
B5 |
ASTM A193 Grade B5 |
AISI 501 | 1/4 Thru 4 | -- | 80,000 | 100,000 |
|
B6 |
ASTM A193 Grade B6 |
AISI410 | 85,000 | 110,000 | ||
|
B7 |
ASTM A193 Grade B7 |
AISI4140,4142, OR 4105 |
1/4 thru 2-1/2 | -- | 105000 | 125000 |
| Over 2-1/2 thru 4 | -- | 95000 | 115000 | |||
|
B16 |
ASTM A193 Grade B16 |
Over 4 thru 7 | -- | 75000 | 100000 | |
|
CrMoVa Alloy Steel |
105000 | 125000 | ||||
| 95000 | 115000 | |||||
|
B8 |
ASTM A193 Grade B8 |
85000 | 100000 | |||
| AISI 304 | 1/4 and larger | -- | 30,000 | 75,000 | ||
|
B8C |
ASTM A193 Grade B8C |
AISI 347 | ||||
|
B8M |
ASTM A193 Grade B8M |
AISI 316 | ||||
|
B8T |
ASTM A193 Grade B8T |
AISI 321 | 1/4 and larger | -- | 30,000 | 75,000 |
|
B8 |
ASTM A193 Grade B8 |
AISI 304 | 1/4 thr 3/4 | -- | 100,000 | 125,000 |
|
B8C |
ASTM A193 Grade B8C |
Strain Hardened | Over 3/4 thru 1 | -- | 80,000 | 115,000 |
|
AISI 347 Strain Hardened |
Over 1 thru 1-1/4 Over 1-1/4 thru 1- 112 |
-- -- |
65,000 50,000 |
105,000 100,000 |
||
|
B8M |
ASTM A193 Grade B8M |
AISI 316 Strain Hardened |
95,000 | 110,000 | ||
| 80,000 | 100,000 | |||||
| 65,000 | 95,000 | |||||
| 50,000 | 90,000 | |||||
|
B8T |
ASTM A193 Grade B8T |
AISI 321 Strain Hardened |
100,000 | 125,000 | ||
| 80,000 | 115,000 | |||||
| 65,000 | 105,000 | |||||
| 50,000 | 100,000 | |||||
|
L7 |
ASTM A320 Grade L7 |
AISI4140, 4142 or 4145 |
1/4 thru 2-1/2 | -- | 105,000 | 125,000 |
|
L7A |
ASTM A320 Grade L7A |
AISI 4037 | ||||
|
L7B |
ASTM A320 Grade L7B |
AISI 4137 | ||||
|
L7C |
ASTM A320 Grade LC7 |
AISI 8740 | ||||
|
L43 |
ASTM A320 Grade L43 |
AISI 4340 | 1/4 thru 4 | -- | 105,000 | 125,000 |
|
B8 |
ASTM A320 Grade B8 |
AISI 304 | 1/4 and larger | 30,000 | 75,000 | |
|
B8C |
ASTM A320 Grade B8C |
AISI 347 | ||||
|
B8T |
ASTM A320 Grade B8T |
AISI 321 | ||||
|
B8F |
ASTM A320 Grade B8F |
AISI 303 or 303Se |
||||
|
B8M |
ASTM A320 Grade B8M |
AISI 316 | ||||
|
B8 |
ASTM A320 Grade B8 |
AISI 304 | 1/4 thru 3/4 | -- | 100,000 | 100,000 |
|
B8C |
ASTM A320 Grade B8C |
AISI 347 | Over 3/4 thru 1 | -- | 80,000 | 80,000 |
|
B8F |
ASTM A320 Grade B8F |
AISI 303 or 303Se |
Over 1 thru 1-1/4 | -- | 65,00 | 65,00 |
|
B8M |
ASTM A320 Grade B8M |
AISI 316 |
Over 1-1/4 thru 1- 1/2 |
-- | 50,00 | 50,00 |
|
B8T |
ASTM A320 Grade B8T |
AISI 321 | ||||
 |
SAE J429 Grade 5 |
Medium Carbon Steel, Quenched and Tempered |
1/4 thru 1 | 85,000 | 92,000 | 120,000 |
| ASTM A449 | Over 1 to 1-1/2 | 74,000 | 81,000 | 105,000 | ||
| 1/4 thru 1 | 85,000 | 92,000 | 120,000 | |||
| Over 1 to 1-1/2 | 74,000 | 81,000 | ||||
| Over 1-1/2 thru 3 | 55,000 | 58,000 |
105,000 90,000 |
|||
 |
SAE J429 Grade 5.1 |
Low or Medium Carbon Steel, Quenched and Tempered |
No.6 thru 3/8 |
85,000 | -- | 120,000 |
 |
SAE J429 Grade 5.2 |
Low Carbon Martensitic Steel, Quenched and Tempered |
1/4 thru 1 | 85,000 | 92,000 | 120,000 |
 A325 |
ASTM A325 Type 1 |
Medium Carbon Steel, Quenched and Tempered |
1/2 thru 1 | 85,000 | 92,000 | 120,000 |
| 1-1/8 thru 1-1/2 | 74,000 | 81,000 | 105,000 | |||
 A325 |
ASTM A325 Type 2 |
Low Carbon Martensitic Steel, Quenched and Tempered |
1/2 thru 1 | 85,000 | 92,000 | 120,000 |
|
A325 |
ASTM A325 Type 3 |
Atmospheric Corrosion Resisting Steel, Quenched and Tempered |
1/2 thru 1 | 85,000 | 92,000 | 120,000 |
| 1-1/8 thru 1-1/2 | 74,000 | 81,000 | 105,000 | |||
 BB |
ASTM A354 Grade BB |
Alloy Steel, Quenched and Tempered |
1/4 thru 2-1/2 | 80,000 | 83,000 | 105,000 |
 BC |
ASTM A354 Grade BC |
2-3/4 thru 4 | 75,000 | 78,000 | 100,000 | |
| 105,000 | 109,000 | 125,000 | ||||
| 95,000 | 99,000 | 115,000 | ||||
 |
SAE J429 Grade 7 |
Medium Carbon Alloy Steel, Quenched and Tempered 4 |
1/4 thru1-1/2 | 105,000 | 115,000 | 133,000 |
 |
SAE J429 Grade 8 |
Medium Carbon Alloy Steel, Quenched and Tempered |
1/4 thru 1-1/2 | 120,000 | 130,000 | 150,000 |
|
ASTM A354 Grade BD |
Alloy Steel, Quenched and Tempered 4 |
|||||
 No Grade Mark |
SAE J429 Grade 8.1 |
Medium Carbon Alloy or SAE 1041 Modified Elevated Temperature Drawn Steel | 1/4 thru 1-1/2 | 120,000 | 130,000 | 150,000 |
|
A490 |
ASTM A490 |
Alloy Steel, Quenched and Tempered |
1/2 thru 1-1/2 | 120,000 | 130,000 | 150,000 min |
| 170,000 max | ||||||
|
No Grade Mark |
ISO R898 Class 4.6 |
Medium Carbon Steel, Quenched and Tempered |
All Sizes thru 1-1/2 | 33,000 | 36,000 | 60,000 |
|
No Grade Mark |
ISO R898 Class 5.8 |
55,000 | 57,000 | 74,000 | ||
|
8.8 or 88 |
ISO R898 Class 8.8 |
Alloy Steel, Quenched and Tempered |
85,000 | 92,000 | 120,000 | |
|
10.9 or 109 |
ISO R898 Class 10.9 |
120,000 | 130,000 | 150,000 | ||
Yuyao Meigesi Fastener was established in 2010. It is an export enterprise specializing in the production and sales of fasteners. The company mainly exports various types of screws, nuts, bolts, and other fasteners to more than 50 countries, including Eastern Europe, Western Europe, and South America. Meigesi is built on professionalism, efficiency, integrity, and innovation. After 13 years of operation and development, it enjoys a good reputation in the global fastener industry.
Our company is located near Ningbo Port, offering an excellent geographical advantage. The factory mainly produces self-drilling screws, drywall screws, chipboard screws, and other screw products, with an annual production capacity of 5,000 tons. Equipped with multiple sets of professional advanced production equipment and a product development and quality inspection team, our products are supported by international certifications such as ISO, CE, and ETA. The company’s own brand, Rhino, enjoys a high reputation in the global fastener market.
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