American Bolt Strength and Grade Markings Chart

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Bolt Strength and Grade Markings Chart – Inch Steel Bolts
Head Marking Bolt Grade / Specification Material Nominal Size (Inch) Proof Load psi Tensile Strength Min psi Yield Strength Min psi Rockwell Hardness Min/Max
SAE J429 - Grade 1 Head Markings Grade 1 – SAE J429
Bolts, Screws and Studs
Low or medium carbon steel 1/4″ – 1-1/2″ 33,000 60,000 36,000 B70 / B100
SAE J429 - Grade 2 Head Markings Grade 2 – SAE J429
Bolts, Screws and Studs
Low or medium carbon steel 1/4″ – 3/4″
>3/4″ – 1-1/2″
55,000
33,000
74,000
60,000
57,000
36,000
B80 / B100
B70 / B100
Grade 5 Bolt Markings Grade 5 – SAE J429
Bolts, Screws and Studs
Medium carbon steel or carbon steel with additives, quenched and tempered 1/4″ – 1″
>1″ – 1-1/2″
85,000
74,000
120,000
105,000
92,000
81,000
C25 / C34
C19 / C30
Grade 5.1 Bolt Markings Grade 5.1 – SAE J429
Sems
Low or medium carbon steel, quenched and tempered No. 4 – 5/8″ 85,000 120,000 92,000 C25 / C40
Grade 5.2 Bolt Markings Grade 5.2 – SAE J429
Bolts, Screws and Studs
Low carbon Boron steel, quenched and tempered 1/4″ – 1″ 85,000 120,000 92,000 C26 / C36
Grade 8 Bolt Markings Grade 8 – SAE J429
Bolts and Screws
Medium carbon / alloy steel with additives, quenched and tempered 1/4″ – 1-1/2″ 120,000 150,000 130,000 C33 / C39
Grade 8.2 Bolt Markings Grade 8.2 – SAE J429
Bolts and Screws
Low carbon Boron steel, quenched and tempered 1/4″ – 1″ 120,000 150,000 130,000 C33 / C39
L9 Bolt Markings L9 – Grade 9
Bolts, Nuts and Washers
Hight strength alloy steel 1/4″ – 1-1/2″ 145,000 180,000 155,000 C38 / C42
307A Bolt Markings ASTM A307 Grade A
Bolts, Screws and Studs (General Engineering)
Low or medium carbon steel 1/4″ – 4″ 33,000 60,000 36,000 B69 / B100
307B Bolt Markings ASTM A307 Grade B
Bolts, Screws and Studs (Flanged Joints)
Low or medium carbon steel 1/4″ – 4″ 33,000 60,000 36,000 B69 / B95
A325 Bolt Markings ASTM A325 Type 1
High strength structural bolts
Medium carbon steel, quenched and tempered 1/2″ – 1″
1-1/8″ – 1-1/2″
85,000
74,000
120,000
105,000
92,000
81,000
C24 / C35
C19 / C31
A325 Type 2 Bolt Markings ASTM A325 Type 2
High strength structural bolts
Low carbon Martensitic steel, quenched and tempered 1/2″ – 1″
1-1/8″ – 1-1/2″
85,000
74,000
120,000
105,000
92,000
81,000
C24 / C35
C19 / C31
A325 Type 3 Bolt Markings ASTM A325 Type 3
High strength structural bolts
Atmospheric corrosion-resistant steel, quenched and tempered 1/2″ – 1″
1-1/8″ – 1-1/2″
85,000
74,000
120,000
105,000
92,000
81,000
C24 / C35
C19 / C31
ASTM A354 Grade BB Bolt Markings ASTM A354 Grade BB
Bolts and studs
Alloy steel, quenched and tempered 1/4″ – 2-1/2″
> 2-1/2″ – 4″
80,000
75,000
105,000
100,000
83,000
78,000
C26 / C36
C22 / C33
ASTM A354 Grade BC Bolt Markings ASTM A354 Grade BC
Bolts and studs
Alloy steel, quenched and tempered 1/4″ – 2-1/2″
> 2-1/2″ – 4″
105,000
95,000
125,000
115,000
109,000
99,000
C26 / C36
C22 / C33
ASTM A354 Grade BD Bolt Markings ASTM A354 Grade BD
Bolts, screws and studs
Alloy steel, quenched and tempered 1/4″ – 2-1/2″
> 2-1/2″ – 4″
120,000
105,000
150,000
140,000
130,000
120,000
C33 / C39
C31 / C39
ASTM A449 Type 1 Bolt Markings ASTM A449 Type 1
Bolts, screws and studs
Medium carbon steel, quenched and tempered 1/4″ – 1″
>1 – 1-1/2″
85,000
74,000
120,000
105,000
81,000
58,000
C25 / C34
C19 / C30
ASTM A449 Type 2 Bolt Markings ASTM A449 Type 2
Bolts, Screws and studs
Low carbon Martensitic steel, quenched and tempered 1/4″ – 1″ 85,000 120,000 58,000 C25 / C34
ASTM A490 Type 1 Bolt Markings ASTM A490 Type 1
High strength structural bolts
Medium carbon alloy steel, quenched and tempered 1/2″ – 1-1/2″ 120,000 150,000 min
170,000 max
130,000 C33 / C38
ASTM A490 Type 2 Bolt Markings ASTM A490 Type 2
High strength structural bolts
Low carbon Martensitic steel, quenched and tempered 1/2″ – 1″ 120,000 150,000 min
170,000 max
130,000 C33 / C38
ASTM A490 Type 3 Bolt Markings ASTM A490 Type 3
High strength structural bolts
Atmospheric corrosion-resistant steel, quenched and tempered 1/2″ – 1-1/2″ 120,000 150,000 min
170,000 max
130,000 C33 / C38
Note: Manufacturer’s identification mark are also stamped when applicable.

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Bolt Strength and Grade Markings Chart – Metric Bolts
Head Marking Class and
Material
Nominal Size Range
(mm)
Mechanical Properties
Proof Load
(MPa)
Min. Yield Strength
(MPa)
Min. Tensile Strength
(MPa)
8.8 Class 8.8Medium carbon steel, quenched and tempered All sizes below 16mm 580 640 800
16mm – 72mm 600 660 830
10.9 Class 10.9Alloy steel, quenched and tempered 5mm – 100mm 830 940 1040
12.9 Class 12.9Alloy steel, quenched and tempered 1.6mm – 100mm 970 1100 1220
Usually Stamped A-2 or A-4 A-2 & A-4 StainlessSteel alloy with chromium and nickel All sizes thru 20mm N/A 210 Min.
450 Typical
500 Min.
700 Typical

Important FAQ’s of Bolt Strength and Grade Markings

Q: What are the different strengths of bolts?

Ans: There are several grades of bolts but the three common grades for SAE are 2, 5 and 8. The common class (grades) for metric are 5.8, 8.8, 10.9 and 12.9. Each grade has a specific bolt strength. No matter the system used to grade the bolts, the higher number means the stronger the bolt.

Q: What are bolt grade markings?

Ans: There are several grades of bolts but the three common grades for SAE are 2, 5 and 8. The common class (grades) for metric are 5.8, 8.8, 10.9 and 12.9. Each grade has a specific bolt strength. No matter the system used to grade the bolts, the higher number means the stronger the bolt.

Q: How can you tell the strength of a bolt?

Ans: 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.

Q: What does 8.8 on a bolt mean?

Ans: A property class (PC) is the metric equivalent of a grade in inch series terminology. … So, in English, a PC 8.8 bolt is a bolt with a nominal tensile strength of 800 MPa and a nominal yield strength that is 80% of the bolt’s nominal tensile strength, or 640 MPa.

Q: Is a 10.9 bolt stronger than Grade 8?

Ans: 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.

Q: What are bolt grade markings?

Ans: There are several grades of bolts but the three common grades for SAE are 2, 5 and 8. The common class (grades) for metric are 5.8, 8.8, 10.9 and 12.9. Each grade has a specific bolt strength. No matter the system used to grade the bolts, the higher number means the stronger the bolt.

Q: Is grade A the same as Grade 5?

Ans: There are so many different grades and fasteners all look about the same, medium carbon and alloy steel strength grades are marked for identification.

Q: Which bolts are the strongest?

Ans: Grade 9 structural bolts, also known as grade 9 hex cap screws, are one the strongest structural bolts that can be used today. While the typical grade 8 bolt has a tensile strength of 150,000 PSI, a grade 9 bolt has a tensile strength of 180,000PSI.

NOTES:
1. In addition to the indicated grade marking, all grades, except A563 Grades O, A, and B, must be marked for manufacturer
identification.
2. The markings shown for all grades of A194 nuts are for cold‐formed and hot‐forged nuts. When nuts are machined from bar stock the
nut must be additionally marked with the letter “B.”
3. Nuts are not required to be marked unless specified by the purchaser. When marked, the identification marking shall be the grade
letter O, A, or B.
4. Properties shown are those of non‐plated or non‐coated coarse‐thread hex nuts.
5. Properties shown are those of coarse‐thread heavy hex nuts.
6. Properties shown are those of coarse‐thread heavy hex nuts.
7. Properties shown are those of coarse 8‐thread heavy hex nuts.
8. Harnesses are Brinell Hardness numbers.
9. The nut manufacturer, at his option, may add other markings to indicate the use of atmospheric‐corrosion‐resistant steel.
10. Nuts that are carbide‐solution‐treated require additional letter A–8A or 8MA.
11. Specifications:
ASTM A563: Carbon and Alloy Steel Nuts
ASTM A194/A194M: Carbon and Alloy Steel Nuts for Bolts for High‐Pressure and High‐Temperature Service
Other, less common, grades exist but are not listed her

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