STEEL HEX BOLT GRADES AND MARKINGS


Steel hex bolts are available in different strength grades as designated by the ASTM and SAE. The most common grade markings are Grade 2, Grade 5 and Grade 8 for steel bolts. The identification marking on the head of the steel bolt specifies the grade of bolt. Mechanical properties of steel bolts are given in the following chart with associate identification markings and bolt grades.

Strength values which are given in the following chart are also being used in Bolt Torque Calculator for bolt torque, preload and thread stripping calculations.


Mechanical Properties of Steel Bolts
Identification Grade Material Size (in) Min. Strength (10^3 psi)
Proof Tensile Yield
Bolt Mark Identifier Grade 2 and Grade 4 SAE Grade 1 Low or medium carbon 1/4 to 3/2 33 60 36
ASTM A307 Low carbon 1/4 to 3/2 33 60 36
SAE Grade 2 Low or medium carbon 1/4 to 3/4 55 74 57
7/8 to 3/2 33 60 36
SAE Grade 4 Medium carbon, cold drawn 1/4 to 3/2 65 115 100
Bolt Mark Identifier Grade 5 SAE Grade 5 Medium carbon, quench and temper 1/4 to 1 85 120 92
ASTM A449 9/8 to 3/2 74 105 81
ASTM A449 7/4 to 3 55 90 58
Bolt Mark Identifier 5.2 SAE Grade 5.2 Low-carbon martensite, quench and temper 1/4 to 1 85 120 92
Bolt Mark Identifier A325 Type 1 ASTM A325, Type 1 Medium carbon, quench and temper 1/2 to 1 85 120 92
9/8 to 3/2 74 105 81
Bolt Mark Identifier A325 Type 2 ASTM A325, Type 2 Low-carbon martensite, quench and temper 1/2 to 1 85 120 92
9/8 to 3/2 74 105 81
Bolt Mark Identifier A325 Type 3 ASTM A325, Type 3 Weathering steel, quench and temper 1/2 to 1 85 120 92
9/8 to 3/2 74 105 81
Bolt Mark Identifier A354 Grade BC ASTM A354, Grade BC Weathering steel, quench and temper 1/4 to 5/2 105 125 109
11/4 to 4 95 115  
Bolt Mark Identifier SAE Grade 7 SAE Grade 7 Medium-carbon alloy, quench and temper 1/4 to 3/2 105 133 115
Bolt Mark Identifier SAE Grade 8 SAE Grade 8 Medium-carbon alloy, quench and temper 1/4 to 3/2 120 150 130
ASTM A354, Grade BD Alloy steel, quench and temper 1/4 to 3/2 120 150 130
Bolt Mark Identifier SAE Grade 8.2 SAE Grade 8.2  Low-carbon martensite, quench and temper 1/4 to 1 120 150 130
Bolt Mark Identifier ASTM A490, Type 1 ASTM A490, Type 1 Alloy steel, quench and temper 1/2 to 3/2 120 150 130
Bolt Mark Identifier ASTM A490, Type 3 ASTM A490, Type 3 Weathering steel, quench and temper

Note: Minimum strengths are strengths exceeded by 99 percent of fasteners.

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