July 4, 2022

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How do you identify a bolt grade?

5 min read

Asked by: Robert Pratama

You can usually figure out the grade, or strength, of a bolt by looking at the markings on its head. English bolts (U.S.S. or S.A.E) are categorized by grade, from grade 2 to grade 8, where the grade represents inch strength. The higher the grade, the stronger the bolt.

How can I tell what grade a bolt is?

The property class is expressed in raised or depressed numerals on top or on the side of the bolt head. ASTM Bolt Grades—The ASTM grade standard is set by the American Society for Testing and Materials. Its strength grades are indicated by the letter A plus three numerals stamped on the bolt head.

What does the 8.8 on a bolt mean?

So, in English, a Property Class 8.8 bolt is a bolt with a nominal tensile strength of 800 MPa and a nominal yield strength that is 80% of that nominal tensile strength, so 640 MPa.

What do the letters on bolts mean?

The three-letter code is the manufacturer code (for example, HKT stands for Hau Kwang Enterprises) and the numbers (if metric) or radial lines (if SAE) refer to the bolts’ strength. If there are no numbers or lines present, assume the bolt is no better than a grade 2 (low strength).

Is Grade 8 or 8.8 Stronger?

Table 1.

Grade/Class Strength
Grade 5 Medium strength.
Grade 8 High strength.
Metric Class 4 Similar to Grade 2.
Metric Class 8.8 Similar to Grade 5.

How can you tell if a bolt is a Grade 5?

The higher the grade, the stronger the bolt. English bolts have radial lines on their head to identify the grade, or strength class. The number of lines on the bolt head is 2 less than the actual grade. So, for example, a grade 5 bolt will only have 3 radial lines on its head.

What does 4.6 mean on a bolt?

In 4.6, The first number 4 indicates 1/100 of nominal tensile strength . Hence the tensile strength = 400 Mpa. The second number indicates 10 times the ratio between lower stress(proof stress) and nominal tensile strength(yield stress ratio) means, 10 times the yield stress = 10 x 240/400 = 2400/400 = 6.

Are stainless bolts stronger than Grade 8?

Stainless Steel Grades & Strength



Bolt strength is rated in PSI (pounds per square inch). A stainless steel bolt has the same PSI rating as a grade 5 bolt (125,000 PSI). A grade 8 bolt has a stronger rating with a PSI of 150,000.

Is a 10.9 bolt stronger than Grade 8?

Class 10.9 is stronger than class 8.8. It is commonly found in high strength automotive applications. Class 10.9 is similar to grade 8.

What is M in bolt size?

The letter ‘M’ indicates that this bolt uses a metric thread. The number ‘8’ refers to the nominal diameter of the bolt shaft in millimeters. The number 1.0 is the thread pitch of the bolt, which is the distance between threads, in millimeters. And the final figure, 20, is the length in millimeters.

What does M12 mean on a bolt?

The first half (M12), is the size measurement (metric) taken across the outside diameter of the thread (which in this case is 12mm). The second half is the thread pitch, which is the measurement of threads/inch (which in this case is 1.75).

Does M10 mean 10mm?

If the size is M10 x 25, that would mean that the diameter is 10 mm.

How do you read bolt sizes?

So when you read a bolt that says quarter 20 by 2 that means quarter inch diameter 20 TPI that's threads per inch which would be here.

What does M14 mean on a bolt?

M14 means it is metric with a 14mm outside diameter.

How do you specify a bolt?

The size of a metric bolt is specified using pitch, diameter, and length in millimeters. For example, in M8-1.0*20, the “M” means the Metric thread designation, the digit 8 refers to the Nominal diameter (in millimeters), 1.0 refers to the pitch, and 20 refers to the length.

How do you read a bolt head?

When you're talking about a grade 5. You always want to see 3 radial slashes on the top of the head that mark is a grade.

What do the numbers on top of a bolt mean?

The first number in each size is the nominal or root (minor) diameter (mm) and the second number is the thread pitch (mm). NOTE: Remember that the nominal bolt diameter is the measurement of the bolt diameter as taken from the bottom of the threads NOT the top (which would be major diameter).

What does 7 on a bolt head mean?

The marks approximately correspond to the following property classes: Head Mark “4”: 4.6, 4.8, 5.6, 5.8, 6.8. Head Mark “7”: 8.8. Head Mark “8”: 9.8.

What does 4.8 mean on a bolt?

For example, a bolt with a performance grade of 4.8 means:



The nominal tensile strength of bolt material is 400 MPa. The yield-strength ratio of bolt material is 0.8. The nominal yield strength of bolt material is 400 x 0.8=320 MPa.

What does 48 on the head of a bolt mean?

For instance, a UTS bolt labeled #3-48 is a gauge 3 bolts or screw with 48 threads per inch, and a 1/4-20 screw has a 1/4 inch diameter and 20 threads per inch.

What does 9.8 on a bolt mean?

Higher Number Means Stronger



The higher the ISO numbers are, the stronger the bolt. A metric bolt designated as ISO class 6.8 roughly corresponds in strength to an SAE Grade 2 bolt. Bolts of ISO class 8.8 and the slightly stronger class 9.8 roughly correspond to an SAE Grade 5 bolt.

What grade is an 8.8 bolt?

High tensile steel bolts



Grade 8.8 high tensile steel is often referred to as the structural grade for bolts. It is the most common form of high tensile material and is usually stocked in plain finish or zinc. It can be plated in many other coatings.

Is Grade 8 or 12.9 stronger?

Used in high stress environments, grade 12.9 fasteners are the highest class of metric cap screws. Where Grade 8 fasteners have a 150,000 psi tensile strength, 12.9 fasteners have a 180,000 psi tensile strength, making them more durable than the grade 5.

What does 10.9 on a bolt mean?

The number which appears after the decimal, when multiplied by 10, will provide the approximate yield strength percentage in relation to the minimum tensile strength. For the 10.9 bolt, the 9 tells the user that the yield strength of the bolt is approximately 90% of the first number: 1,000 MPa.

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