What do the numbers on the head of a bolt mean?

Asked by: Melody Johnson

You can usually figure out the grade, or strength, of a bolt by looking at the markings on its head. English bolts (U.S.S. or S.A.E) are categorized by grade, from grade 2 to grade 8, where the grade represents inch strength. The higher the grade, the stronger the bolt.

What do the numbers mean on the top of a bolt?

The number has nothing to do with the size, but does indicate the relative strength of the bolt. The higher the number, the stronger the bolt. Some metric nuts are also marked with a single-digit number to indicate the strength, and some may have the M and strength grade embossed on the flats of the hex.

What does 8.8 mean on a bolt head?

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 do the markings on a bolt head 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.

What does the number 7 on a bolt head mean?

The marks approximately correspond to the following property classes: Head Mark “4”: 4.6, 4.8, 5.6, 5.8, 6.8. Head Mark “7”: 8.8. Head Mark “8”: 9.8. #2.

Is Grade 8 or 10.9 stronger?

Class 10.9 is stronger than class 8.8. It is commonly found in high strength automotive applications. Class 10.9 is similar to grade 8.

Is Grade 8 or 12.9 stronger?

Used in high stress environments, grade 12.9 fasteners are the highest class of metric cap screws. Where Grade 8 fasteners have a 150,000 psi tensile strength, 12.9 fasteners have a 180,000 psi tensile strength, making them more durable than the grade 5.

Is Grade 8 or 8.8 Stronger?

Table 1.

What is the strongest bolt grade?

grade 8

Grade 9 Bolts
Grade 9 structural bolts, also known as grade 9 hex cap screws, are one the strongest structural bolts that can be used today. While the typical grade 8 bolt has a tensile strength of 150,000 PSI, a grade 9 bolt has a tensile strength of 180,000PSI.

What does 10.9 bolt mean?

Grade 10.9 metric bolts are manufactured using medium carbon steel, medium carbon steel alloy and low carbon boron steel that has been quenched and tempered. Used in automotive applications and for bolting large and forged parts, metric 10.9 bolts exhibit high tensile strength and good wear resistance.

Is a Grade 8 bolt strong?

Grade 8 bolts are designated as a 150 ksi. This means its tensile strength or the resistance it has before it is subject to breaking under tension is equal to 150,000 lbs. per square inch. In comparison, a Grade 5 bolt is weaker as its tensile is 120 ksi, placing it at 120,000 lbs.

What does 9.8 mean on a bolt?

Higher Number Means Stronger

The higher the ISO numbers are, the stronger the bolt. A metric bolt designated as ISO class 6.8 roughly corresponds in strength to an SAE Grade 2 bolt. Bolts of ISO class 8.8 and the slightly stronger class 9.8 roughly correspond to an SAE Grade 5 bolt.

Is a Grade 5 bolt strong?

Manufactured from medium carbon steel and hardened for greater strength and durability, a grade 5 bolt is distinguished by 3 radial lines and promises tensile strengths between 105,000 and 120,000 psi. They are most commonly found in automotive applications or those that require medium strength.

Should I use Grade 5 or Grade 8 bolts?

Grade 8 bolts have been hardened more than grade 5 bolts. Thus they are stronger and are used in demanding applications such as automotive suspensions. Grade 8 bolts have 6 evenly spaced radial lines on the head.

Is stainless or Grade 8 stronger?

A stainless steel bolt has the same PSI rating as a grade 5 bolt (125,000 PSI). A grade 8 bolt has a stronger rating with a PSI of 150,000.

Can Grade 8 bolts rust?

Grade 8 bolts have 6 evenly spaced radial lines on the head.” Unlike stainless steel, which is highly resistant to corrosion, steel, however reinforced, will oxidize over time and rust. Grade 8 bolts that are not galvanized or plated with yellow zinc, however, are cheaper.

What are yellow screws for?

Yellow Zinc Plated Finish Screws, Fasteners and Fixings

A yellow plated zinc finish gives a fixing a protective layer, providing a good level of corrosion prevention, as well as further protection due to the passivate addition which provides a yellow or gold finish.

Which is better zinc or stainless steel?

Though some Zinc alloys can be very strong, overall stainless steel is stronger. However, zinc is a heavy element, and when alloyed with other metals it provides better corrosion resistance, stability, dimensional strength and impact strength.

Is yellow zinc better than zinc?

Yellow zinc is most commonly used for automotive parts because it provides a good level of corrosion resistance. Black zinc offers a little less corrosion resistance than yellow zinc. Blue or clear zinc plating provides the least amount of corrosion resistance.

Will Grade 5 bolts rust?

Steel fasteners are available in grade 2, grade 5, grade 8, and alloy steel and are usually plated with a slightly bluish or yellow zinc coating, or are galvanized to resist corrosion. There are other grades but they are not used very often. The grade is marked on the head of the bolt.

Is black oxide better than zinc plated?

Zinc plating offers sacrificial protection against corrosion and black oxide does not. Black oxide has no rust resistance except its wax or oil.

How can you tell if a bolt is zinc plated?

Hot dip galvanising or zinc plating can be used on anything from small nuts and bolts to large beams for buildings. The steel is put in a big bath, where the coating is applied. If it’s galvanised, it will be dull grey and a little rough. A zinc plated product will be shiny and smooth.

What does #8 bolt mean?

Grade 8 – Grade 8 bolts are made from medium carbon alloy steel. The bolts of this grade feature 6 radial lines. The nominal size of the grade 8 bolts can be from 1/4″ to 1 1/2″. The minimum yield strength of this grade bolt is 130,000 psi.

How do I know if I have a m6 or M8 bolt?

The defined diameter of metric bolts is actually slightly larger than the actual diameter of the bolt shaft. So an M8 bolt would have a shaft diameter that’s slightly under 8mm which means that the bolt should fit through an 8mm hole.

Which is better zinc plated or galvanized?

Zinc plating (also known as electro-galvanising) is a process where zinc is applied by using a current of electricity. While is does provide some rust protection, its thinner coating is not as rust resistant as hot dip galvanising. Its main advantage is it is cheaper and easier to weld.

What kind of bolts do not rust?

Stainless steel, aluminum, and zinc screws won’t rust. One of the best options is stainless steel screws because it’s been developed to be highly resistant to rust and corrosion. Aluminum and zinc screws are also highly resistant to rust.

How long will zinc bolts last outside?

12 months

Zinc-plated bolts and hardware fittings, such as gate hinges, will not provide adequate protection from corrosion, and usually do not last beyond 12 months in outdoor settings such as urban coastal environments.