# What do the markings on bolt heads mean?

## What do the markings on bolt heads mean?

The markings can identify the standard to which the bolt was made. For instance, if a bolt head contains three radial lines, then it’s a Grade 5 bolt. If it contains five radial lines, then the bolt is Grade 8.

## How do you read metric bolts?

Metric Bolt Sizes

1. The letter ‘M’ indicates that this bolt uses a metric thread.
2. The number ‘8’ refers to the nominal diameter of the bolt shaft in millimeters.
3. The number 1.0 is the thread pitch of the bolt, which is the distance between threads, in millimeters.
4. And the final figure, 20, is the length in millimeters.

Strength Grades for metric fasteners are designated by a symbol comprised of 2 numbers, separated by a decimal. For example, 4.6 and 8.8. The first number represents 1/100 of the nominal tensile strength in N/mm^2.

How do you tell what grade a metric bolt is?

Metric Bolt Grades—Metric grades are set according to rules set by the ISO (International Standards Organization). The grades consist of two numbers separated by a dot. The property class is expressed in raised or depressed numerals on top or on the side of the bolt head.

### How do you measure a bolt metric?

Do not measure the head of the bolt, measure the threaded part, outside of the threads. If your bolt is metric, then the diameter is stated using the letter “M”. For example, if your bolt has a diameter of 4mm then it is called an ‘M4 bolt’ if your bolt is imperial then it will be measured in inches.

### What do the numbers mean on metric bolts?

The letter ‘M’ indicates that this bolt uses a metric thread. The number ‘8’ refers to the nominal diameter of the bolt shaft in millimeters. The number 1.0 is the thread pitch of the bolt, which is the distance between threads, in millimeters. And the final figure, 20, is the length in millimeters.

What does 8.8 mean on metric bolts?

So, in English, a Property Class 8.8 bolt is a bolt with a nominal tensile strength of 800 MPa and a nominal yield strength that is 80% of that nominal tensile strength, so 640 MPa.

What size is M6 in mm?

6 mm
M6 refers to a metric 6 mm screw. The outside diameter of the threads is 6 mm. The standard metric rack screw is actually an M6 x 0.1 mm. The number 0.1 mm refers to 0.1 threads per millimeter.

## What does A325 bolt mean?

ASTM A325 is an ASTM International standard for heavy hex structural bolts, titled Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. It defines mechanical properties for bolts that range from 1⁄2 to 11⁄2 inches (13 to 38 mm) in diameter.

## Is SAE metric or imperial?

The SAE (Society of Automotive Engineers) system uses inches, and the imperial or metric system uses millimeters.

Is SAE standard or metric?

The origin of the SAE standard comes from the English, or Imperial, system, which is based on inches and the fractions thereof. SAE, which stands for the Society of Automotive Engineers, was used as the standard primarily on U.S.-made cars and trucks through the 1970s.