US Bolt Grades and Their Head Markings

There are a lot of things to consider when looking at bolts. Length, diameter, thread pitch; these are all important things to keep in mind.

Usually, there are letters or numbers engraved on the head of each bolt to indicate their grade, material type and dimensions. These markings are a helpful tool for tracing back to the manufacturer should there be any problems with the bolt.
Grade 5

Grade 5 bolts are made from medium strength carbon steel and are heat treated to provide increased strength. They also offer improved corrosion resistance, making them suitable for a variety of environments.

Contractors, designers, OEMs and maintenance staff often choose these bolts for non-critical joints or applications due to their affordability. They are identified by a head marking that consists of three slashes or the manufacturer’s letters.
Grade 8

Grade 8 bolts are high-strength and durable, making them ideal for heavy duty applications. They’re made from medium carbon alloy steel that is heat-treated, quenched and tempered. They have a proof load of 120,000 psi and are identified by the head marking of 6 radial lines.

They’re commonly used in construction and automotive applications. Look for USA made bolts with traceable documentation that gives you info like lot code, date of manufacture and heat treat batch data.
Grade 9

A grade 9 bolt is one of the strongest structural bolts that can be used today. They are also more resistant to corrosion than their grade 8 counterparts.

They can be identified by their finished hex bolt design and require heavy hex nuts. They’re ideal for use on heavy construction projects that require extra strength. They have a minimum tensile strength of 150,000 psi.
Grade 10

Grades for bolts and screws are determined by a number of factors, including their tensile strength. This article explains the different grades of standard and metric bolts, and their head markings.

A bolt head marking of 4.6 indicates that the fastener has a tensile strength of 60,000 to 74,000 psi. It is most commonly used in automotive applications and other medium-strength projects.
Grade 11

Identified by 3 radial lines, these bolts are made from medium carbon steel and case hardened for added strength. They are often used in automotive applications.

Understanding the tensile strength, yield strength, and proof load of fasteners is important to make sure you’re selecting the right hardware for your project. Learn about these critical characteristics and how to read the markings on a bolt head.
Grade 12

Grade 12 bolts are a high-strength variety that can withstand large amounts of pressure. These bolts are commonly used in construction applications where reliability is crucial.

They can withstand a maximum of 120,000 psi. These bolts are typically made of medium carbon steel and are identified by a series of radial lines engraved on the head.

These bolts are quenched and tempered for increased strength and hardness. They are also marked with their grade and the manufacturer’s identification mark.
Grade 13

Identifying the grade of a bolt by its head markings can help you quickly and easily understand its critical mechanical properties. These include proof load, tensile strength and yield strength.

These fasteners are made from stainless steel with good corrosion resistance. They have a nominal tensile strength of 800 MPa. They are used in applications requiring high strength and endurance. They are heat treated and case hardened.
Grade 14

Bolts, nuts and threaded rods – torque, tension and loads. Diameters and bolt circles for standard ASME B16.5 flanges class 150 to 2500. Dimensions of metric threads according ISO 724. Minimum ultimate tensile and proof loads for metric bolts with coarse or fine threads. Effect of lubrication on bolt tension and torque.

The tensile strength of fasteners is important for making sure they’re strong enough to hold together under load. It’s usually marked on the bolt head along with other information like the proof load and yield strength.
Grade 15

Property class designations are a great way to identify the approximate tensile strength of a fastener. For example, a Property Class 8.8 bolt has a nominal tensile strength of 800 MPa which is about 155 ksi.

Estimated torque values are provided for guidance only. There are many variables that affect the torque-tension relationship like lubrication and assembly conditions. Consult your engineering specifications for proper testing procedures.
Grade 16

Typically, the grade of a bolt will indicate its tensile strength. Marsh Fasteners explains the different grades of SAE bolts and how to choose the right ones for your application.

Identified by 3 radial lines, these bolts are made from medium carbon steel and have been case hardened for added strength. They are suitable for heavy manufacturing applications. They’re also corrosion resistant.US bolts

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