A bolt.
he diameter of the bolt.
a grade 8 bolt is stronger, about twice as strong.
If there are lines coming inward from the outside on the head then this is an SAE bolt, not metric. If there are three of these lines than it is a grade five bolt.
A grade 5 hex bolt has 3 radial lines formed into the top of the head. Bolt manufacturers can provide listings of bolt markings and their corresponding strength ratings.
It's a measure of the strength of the bolt. The strength is measured using what's called a grade. In this case, you have a grade 8 bolt. The higher the number, the stronger the bolt.
The strength of a bolt is typically specified by its grade, and the strongest commonly used bolt grades are Grade 8.8, Grade 9.8, Grade 10.9, and Grade 12.9. These grades are commonly used in construction, automotive, and engineering applications. Bhansali Fasteners is one of the leading Bolts Manufacturers in India.
grade refers to composition and strength. Generally a higher Grade ( number or alphabet) is a stronger material. For example Grade C is stronger than Grade A Grade 8 bolt is stronger than grade 5 bolt.
An SAE Grade 8 bolt will have 6 radial lines on it as shown below. \ | / / | \
Hardness
numbers
It signifies the grade of a bolt. For a load bearing bolt where it's failure could cause injury or damage, you should use a high grade bolt. 5-9 are higher grades.