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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.

Differences Between Fastener Grades
SAE Grade 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