BOLT HEAD IDENTIFICATION MARKINGS

The following table will give you a good idea of the type of bolt that you have by the markings on the head of the bolt. This system is based on the SAE and ASTM standards of manufacturing.

 However, you must be cautious as some oversees imports may use these marking indiscriminately and they may not actually be the same as listed in this table. If in doubt about the source of the bolt, please contact a reputable fastener distributor. The information provided is for reference only.

Grade
Marking

Spec.

Material

Bolt &
Screw Size

Proof
Load
PSI

Tensile
Strength
Min PSI

SAE-Grade 1 

Low Carbon Steel 

1/4" - 1-1/2" 

33,000

60,000

ASTM-A307

Low Carbon Steel 

1/4" - 1/2" 
1-1/2" - 4"  

33,000

60,000
55,000 

SAE-Grade 2 

Low Carbon Steel 

1/4" - 3/4"
3/4" - 1-1/2" 

55,000
33,000 

74,000
60,000 

SAE-Grade 3 

Medium Carbon Steel,
Cold Worked  

1/4" - 1-1/2"
 1/2" - 5/8" 

85,000
80,000 

110,000
100,000 

SAE-Grade 5
ASTM-A 449 

Medium Carbon Steel,
Quenched & Tempered 

1/4" - 1"
Over 1" - 1-1/2"
Over 1-1/2" - 3" 

85,000
74,000
55,000 

120,000
105,000
090,000

ASTM-A 325 

Medium Carbon Steel,
Quenched & Tempered 

1/2", 5/8", 3/4"
7/8", 1"
1-1/8" - 1-1/2" 

85,000
78,000
74,000 

120,000
115,000
105,000 

ASTM-A 354
Grade BB 

Low Alloy Steel,
Quenched & Tempered 

1/4" - 2-1/2"
Over 2-1/2" - 4" 

80,000
75,000 

105,000
100,000 

ASTM-A 354
Grade BC

Low Alloy Steel,
Quenched & Tempered 

1/4" - 2-1/2"
Over 2-1/2" -4" 

105,000
095,000 

125,000
115,000 

SAE-Grade 5.1

Low or Medium Carbon 
Steel, Quenched & Tempered,
with Assembled Lock Washer 

Up to 3/8" incl.

85,000

120,000

SAE-Grade 7

Medium Carbon Alloy Steel,
Quenched & Tempered,
Roll Threaded
after Heat Treatment 

1/4" - 1-1/2"

105,000

133,000

SAE-Grade 8

Medium Carbon Alloy
Steel, 
Quenched & Tempered 

1/4" - 1-1/2"

120,000

150,000

ASTM-A 354
Grade BD 

Alloy Steel,
Quenched & Tempered 

1/4" - 1-1/2"

120,000

150,000

ASTM-A 490

Alloy Steel,
Quenched & Tempered 

1/2" - 2-1/2"
Over 2-1/2" - 4" 

120,000
105,000 

150,000
140,000

 

 

 


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