Cap Screw Grade Markings
Identify the Right Fastener for Your Job

Grade 2
(No marks)
Use for wood and general hardware applications

Grade 5
(Three radial lines)
Use for small engine repair and for automotive needs

Grade 8
(Six radial lines)
Automotive needs and other applications where high tensile strength is required

Grade Markings Help You Choose the Right Fastener for Your Project
Head markings on cap screws are your assurance that the fastener you choose will do the job it's designed to do.
The Society of Automotive Engineers and the Industrial Fasteners Institute have established specific ranges of hardness and tensile strength for each grade of fastener. All Elco fasteners meet or exceed these requirements.
There are certain applications which engineers have determined are appropriate for the various grade of fasteners. Do-it-yourselfers can use the grade markings to be sure the bolt or cap screw will meet their requirements.

Grade 2 Fasteners
Often referred to as "hardware" quality, these fasteners are typically made of low-carbon steel. They are ideally suited for holding wood pieces together (in combination with appropriate nuts and washers) or general hardware use where higher strength is not required.
There is no grade marking on the head of Grade 2 fasteners, although many manufacturers will put a distinguishing company identification on the head.

Grade 5 Fasteners
Grade 5 fasteners are made of medium-carbon steel. These fasteners are then quenched and tempered for the additional strength necessary for most automotive uses and other applications where strength is a moderate concern.
The grade marking on the head of a Grade 5 fastener is three equally-spaced lines coming out from the center of the head. Manufacturers` identifications are added for traceability.

Grade 8 Fasteners
Grade 8 fasteners are manufactured of medium-carbon alloy steel for the most demanding applications. These fasteners are then quenched and tempered to superior strength and hardness qualities.
The grade marking on a Grade 8 fastener is six equally spaced lines coming out from the center of the head. Once again, the manufacturer's mark is necessary for traceability.
Do not confuse the use of Grade 8.2 boron bolts with true Grade 8 fasteners. The two grades have different characteristics and should not be used interchangeably.

Diameter

Proof
Load PSI

Tensile
Strength
Min. PSI

Hardness
Rockwell

Material and
Heat Treatment

Grade 2

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

55,000
33,000

74,000
60,000

B80 - B100
B70-8100

Low or medium
carbon steel

Grade 5

1/4" - 1"
1"- 1-1/2

85,000
74,000

120,000
105.000

C25 - C34
C-19 - C30

Medium carbon steel quenched and tempered

Grade 8

1/4" - 1-1/2

120,000

150,000

C33 - C39

Medium carbon alloy
steel quenched
and tempered