Fastener Grades, Strength & Materials
Fastener Material and Finish Information - From Alloy to Zinc
Alloy steel, aluminum, brass, silicon bronze, and stainless steel are just some of the materials that fasteners are manufactured in. The combination of material, treatment, hardening, and coating (aka plating) are essential to determining the strength and appropriate application for each fastener. Already know what kind of material you want to use? Visit our Shop by Materials page to shop only that material!
If you need to replace a nut, washer, bolt or screw it is always recommended to perform an exact or matching swap. If a bolt is stainless steel, we recommend replacing with stainless steel. Furthermore, if a bolt grade is 316 stainless, prized for extra corrosion resistance, we always recommend using 316 when replacing and not a lesser bolt grade such as 304 or 303.
Select a category below to view a picture and information on that type of fastener material or plating methods.
|Stainless Steel ||Silicon Bronze||Brass||Aluminum and Alloy Steel|
|Titanium||Copper and Nickel||Zinc Plated Steel||Fastener Finishes and Plating|
How to Identify a Fastener Material: Understanding Fastener Grades & Materials | Fasteners 101
Understanding Fastener Grades & Materials Transcript
Scroll Down to Continue Reading
Bob: Hey, welcome back to Albany County Fasteners - Fasteners 101. I'm Bob and today we're going to talk about different grades and types of bolts. Let's get started.
I have an array here of different types of materials. I want to go through the materials first and give them the magnetic test. So, I have a magnet here to show you. So first I have a 316 stainless, which is this one here, I have a 18-8 stainless, a brass hex cap screw and a silicon bronze hex cap screw, this is hot-dip galvanized, this is a plain grade eight or better zinc plated hex cap screw, another zinc hex cap screw but in a different grade, so this is just a standard grade, but I'll go through the grades in a second, and I have a grade 8 yellow zinc coated (hex cap screw). I just want to give these a magnet test, so you can see some are magnetized others are not.
This is a 316 stainless and in this situation there's no pull from the magnet. This is an 18-8 which has very little pull, as you can see. Not much but there is some partial magnetic field to that. This is brass. Brass has no magnetic field to it at all. This is silicon bronze. This is also, just so you know, used in heavy salt-water applications such as on boats. This is a heavily used item for fasteners with saltwater day in and day out. No magnetic pull on that. This is a hot dip galvanized hex cap screw. So, this is alloy steel that is just coated with hot-dip galvanized (zinc). You can get some decent corrosion resistance out of that, and you can see, the magnet sticks right to it. Grade 8. This is just a grade 8 plain bolt. Magnetized. Zinc coated or plated. Another zinc plated and then grade 8. You can see all these have heavy magnetism.
I just want to go through the different grades that we have. This is a grade 8 hex cap screw. You can tell by the markings on the head, but I'm going to show you an even better one. This is a large grade 8 bolt and there you can see the markings. These markings on this head indicate, these 1-2-3-4-5-6 slashes that you see here, those slashes indicate that that's a grade 8 bolt.
These letters that you're seeing is the manufacturer's markings, so they can identify, should the bolt fail, they can identify if this is their bolt or not. So typically grade eight, in most cases, is coated in yellow zinc. You can see this bolt, it's coated with a yellow zinc. These are typically, grade eights, are heated to temperatures of 800 degrees. These are very commonly used in situations where you need a very strong bolt.
I have here a grade 5 bolt. You can see these three slashes. So, three slashes on a grade 5 bolt. You'll see again these letters; these again are the manufacturers letters. You can see the grade 8.
This is how you tell the difference. What you're buying. When you go out and you're looking for a grade 5 bolt, you're always looking for the three slashes on the bolt. It's standard through the industry.
This is a grade two bolt. This grade 2 bolt has no markings, no slashes at all. The only thing that you're going to see on here is the manufacturer's initials or their letters.
This is a structural steel bolt, or they call this a structural bolt. You can get structural bolts, structural washers, and structural nuts in A325 (alloy), they have a 520, I think a 524 or 536 in nuts, but this is a structural bolt used in structural steel applications. These typically fall into the ASTM A193 which are typically heated somewhere around 1,600 degrees and treated in that fashion, but I would refer you onto the ASTM. These are also, just so you know, plain and oiled finished. That's the only way they, oh I'm sorry, they do come in hot dip galvanized also, but the most common used is oil finish.
As far as grades go, I was showing you the grades, most plain bolts, other than structural, will have the grade 8 markings on them. Ours are grade eight or better, and that's the way that they're indicated on our website, as grade 8 or better, and you will see the grade 8 slashes on the head. That will indicate, the six slashes will indicate, that that's a grade 8 bolt and it has been treated, heat treated, through-throughout the bolt so it is hard enough not to break for you.
This I spoke to you before, hot-dip galvanized bolts are typically just grade 2 bolts and they are treated and dipped into a hot dip galvanized bath and they're brought out of the bath and then drained.
Silicon bronze is, like I said, mostly used on boats, saltwater applications, they're using electrical panels for many different reasons. This is very common in those applications.
Brass again used in plumbing, hot water, these typically have no heavy strength to them at all. You would find these to be the standard type 2, or equal to type 2 bolts. 18-8 stainless. These are typically heated up to about 650 degrees when they're treated. They can range anywhere from a grade two to a grade five depending upon the manufacturer. This is a grade 316 stainless which is typically the fastener of choice in corrosive environments.
So, silicon bronze is composed of copper, silicon, and other alloys: tin, zinc, iron, magnesium, which makes them corrosion-resistant for marine and freshwater applications and they're used in electrical panels as I mentioned to you.
You'll find alloy steel, which are these here. Alloy steel is made from high-strength steel alloy, heat-treated, so that would be the grade eight. These are all alloys. Grade 8 is heat treated.
These, over-time, just so you know, have a zinc finish on them and they do not have any long-lasting rust resistance at all.
Hot dipped galvanized coat alloy steel. They're dipped in molten zinc. These typically have to have thicker threads. You cannot use a zinc nut with a hot dip galvanized nut, it just won't go on properly and you're going to have problems. So, because of the hot dip galvanizing process, (the zinc) is so thick they have to adjust the threads, so they'd properly coat the thread. There would be rust resistance if hot dip galvanized.
I just wanted to bring up about the brass, it's solid brass and with solid brass it's copper and zinc. There is brass out there that they do use lead in. Lead is used today in many, many brass products. That's why in California there's a prop 65 (warning) that we have to warn that it could be cancerous. We do bring that to everybody's attention in reference to brass. Brass is not always what they say or call a solid product.
I just wanted to bring that to your attention and educate you on the different grades and the different coatings along with different metals that are used, and I just want to brush over the different heat treatments. So, with a grade 8, this falls under the SAE J429. You can look that up to go over on google. Just google that and you'll find all the information in reference to the treatment of a grade 8 bolt. A grade 5 bolt falls under ASTM 574. A grade A325 falls under ASTM specifications also and you can look those up on google to get further information.
That's our video for today.
Stainless steel is used primarily for long lasting applications, due to its corrosion-resistant nature and durability. Scratching or burring the metal will not create surface rust as the corrosion resistance exists within the metal itself. Stainless is a soft metal due to the low carbon content, therefore most stainless steel bolts are cold-formed and not heat treated or thru-hardened. Cold forming and threading cause stainless bolts to become slightly magnetic, some fasteners will be more magnetic than others depending on size and how quick the cold forming process is. Stainless fasteners are typically a clean silver color, which also makes them common in finishing and decorative applications. Stainless Steel should never be used with aluminum, galvanic corrosion is likely to occur.
Stainless steel will not rust due to scratching due to the thin layer of chromium creating an invisible protective layer. This thin layer will rebuild itself in the presence of oxygen. Note: If you are not in an oxygen rich environment the material will take longer to rebuild or not rebuild at all. This will leave it open to possible corrosion. Stainless steel can be broken down into three different types: Austenitic, Martensitic and Ferritic.
Austenitic Stainless Steel
(Between 15%-20% Chromium, Between 5%-19% Nickel) - Austenitic stainless has the highest degree of corrosion resistance of the three types. This type of stainless includes these grades: 302, 303, 304, 304L, 316, 32, 347 and 348. They also have a tensile strength of between 80,000 - 150,000 PSI.
Martensitic Stainless Steel
(Between 12%-18% Chromium) - Martensitic stainless steel is considered a magnetic steel. It can be heat treated to increase its hardness and is not recommended for welding. This type of stainless includes: 410, 416, 420 and 431. They have a tensile strength of between 180,000 and 250,000 PSI.
Ferritic Stainless Steel
(Between 15%-18% Chromium) - Ferritic stainless steel has a tensile strength of 65,000 - 87,000 PSI. While it is still corrosion resistant, it is not recommended for areas where corrosion is likely to occur. This material cannot be heat treated. Due to the forming process it is magnetic and not suitable for welding. Ferritic grades of stainless include: 430 and 430F.
18-8 Stainless Steel:
(18% Chrome, 8% Nickel, .08% Maximum Carbon) - 18-8 Stainless refers to 300 series stainless steel. 303 and 304 Stainless are the most commonly listed grades, the standard grade for stainless fasteners. They are corrosion-resistant and durable. They are often used in marine applications in freshwater environments but will not work as effectively in a salt-water environment as 316 stainless. Stainless alloy resists oxidizing and rusting, however it can tarnish over time. Equivalent to metric A2 Stainless Steel.
305 Stainless Steel:
(17%-19% Chrome, 8%-10% Nickel, .12% Maximum Carbon) - This grade has been developed specifically to improve the cold heading qualities of 18-8. Corrosion resistance and physical qualities are equal to Type 304. 305 stainless steel is most commonly used to make deck screws, which are used to fasten wood or composite boards to the main beams of a deck.
316 Stainless Steel:
(16%-18% Chrome, 10%-14% Nickel, .08% Maximum Carbon, 2.00% Maximum Molybdenum) - This grade of steel is used and recommended for applications in severe, harsh or marine environments. Its corrosion resistance is greater than 18-8 stainless, which is why we recommend using 316 stainless steel fasteners for salt-water application. It is important to remember that even the salt in the air near a body of salt-water can do damage to dry applications, so 316 is the material of choice. Common applications of 316 stainless fasteners include use on boats, docks, piers, and pools.
410 Stainless Steel:
(11.5%-13.5% Chrome, .15% Maximum Carbon) - Since this grade of stainless steel can be hardened up to approximately 40 Rockwell C, it is durable in most environments. Harder than 18-8 stainless but with less corrosion resistance, 410 stainless is commonly used to make roofing screws, siding screws and self-tapping (or self-drilling) screws, because it is a harder material than the metal being fastened in these types of applications.
Below are some of the many bolt grades of stainless steel that we carry.
Is Stainless Steel Magnetic?
Magnetism and Stainless Steel Transcript
Scroll Down to Continue Reading
Bob: Welcome back to Albany County Fastener - Fasteners 101. The question of the day: is stainless steel magnetic? Let's get started.
So I have here some nuts, a lock washer, dowel pin, a hex cap screw with a tap bolt, all of these items here are 316 stainless and you may be able to see that. You'll see that marking on there: 316. You can see it on the nut. It's going to be hard for you to see it on the camera, but on the nut, it's marked as 316. These parts are all 316 stainless. 316 stainless is typically non-magnetic, however there is a challenge and we'll talk about that in a minute.
This is aluminum and this is 304/18-8 stainless and these also have the markings for that. So I get calls all the time from customers questioning: why is this stainless magnetic or partially magnetic? So the answer is that some parts in 316-if you were to buy 316 unformed, untooled, in a stock piece of stainless, it would be non-magnetic. However, when you take a hex cap screw or tap bolt like this that's been put into a cold form machine to work the stainless you're then changing the crystal makeup of the stainless steel and that's what makes it magnetic. So this hex cap screw is magnetic. It's 316 stainless, so you would think that it would be non-magnetic but the fact is that it is magnetic. It doesn't matter if it's made here in the USA, it doesn't matter if it's made in Taiwan, or it's made in India, if it changes the makeup of stainless when you cold form it, that's what makes it magnetic. You're changing the crystal structure of the actual stainless itself and I'm going to demonstrate that to you right now.
I have a magnet here. I'm going to show you that this is magnetic.
Now I'm going to show you a nut, which is stainless 316. A nut is not worked, it's just cut. The sides are cut. Then after it's cut a tap goes in and threads the inside. So there's no twisting, turning, hammering, banging of the stainless. So the crystals in a stainless steel nut are not changed in anyway or form. This will end up being non-magnetic. It will not pick up the magnet at all. Put the magnet on top, it just falls off.
This is a dowel pin in 316 stainless. This is just a plain piece of stock, 5/16 inch diameter dowel pin, and all they do is cut it. Then they just chamfer the edges so there's no bending or twisting of this and you will see its non-magnetic. Not holding. Same thing with this nut, another 316 stainless nut, different size; still non-magnetic.
This is a lock washer and this lock washer has been worked. It's just a piece of straight stock and it's been twisted around a jig to create the size of the lock washer and then it's bent. So this will prove out to be magnetic. That's all the 316 stainless.
304, 18-8, is partially magnetic. Typically it is partially magnetic. There's a lot of false information out there that all stainless steel is non-magnetic. Totally untrue. Really the only one that's non-magnetic, other than some special stainless, is this 316 stainless and that's the stainless you use in salt-water applications and that's the one that you won't find surface corrosion or deep corrosion.
So I'm going to demonstrate now for you this nut and let's see if it picks up the magnet. You will see its partially magnetic; it doesn't hold it very strong. It's not as strong as with the 316. With this it's partially magnetic. So it's like I have to hold it there a second and then pick it up. You'll see it'll just drop off. So that's what they call partially magnetic.
This hex cap screw has been put through a cold form process to make the head. That's what changed the crystal makeup of this hex cap screw thus making it magnetic.
This is a rivet, stainless steel-304 stainless. This whole rivet is worked and the whole crystallization of stainless has been changed; the whole structure. So I'm going to demonstrate for you that this will show up as being highly magnetic.
There it is. That's the Hat part and this is the mandrel. All magnetic.
I'm throwing in here a piece of aluminum. This is an aluminum rivet. An aluminum rivet is obviously a metal that is not magnetic and it will not pick up at all. So if you really want total non-magnetic there's aluminum and that's basically my demonstration of showing you that stainless steel, depending upon how it's been treated, becomes magnetic.
Zinc Plated Steel
Zinc Plated Alloy Steel is a common material that fasteners are manufactured in. Zinc plating creates corrosion resistance and gives the bolts a shiny finish. Zinc plated alloy steel is most often available in Grade A, Grade C, Grade 2, Grade 5 and Grade 8. Untreated alloy steel fasteners are black.
Bolt Grades & Head Markings:
Head markings on a bolt are a quick way to determine bolt grade. Some bolts will have additional markings that indicate the manufacturer; the most prized bolts have clean heads with limited markings.
Grade 2 / Grade A
Grade A and Grade 2 are the most common grades of zinc plated alloy steel. Case hardened low or medium carbon steel. No head markings (manufacturers mark may be included).
Grade C is a thru-hardened medium carbon zinc plated alloy steel. No head markings (manufacturers mark may also be included). Finish is equivalent in strength to Grade 8 but without the yellow color.
Grade 5 alloy steel is a medium carbon zinc plated alloy steel that is heat treated to increase hardness. Grade 5 bolts have three (3) evenly spaced hash marks on the head markings (manufacturers mark may also be included).
Grade 8 / Grade G
Grade 8 zinc plated alloy steel bolts are thru-heated and thru-hardened with a CR+5 zinc plating. This treatment adds a superior strength and corrosion resistance, to the extent that they are often used for armored vehicles and vehicle suspensions. Grade 8 bolts have six (6) evenly spaced hash marks on the head markings (manufacturers mark may also be included).
Silicon bronze fasteners are made of copper, silicon, and various other alloys such as zinc, tin, iron and manganese. The color of silicon bronze may vary based on the amount of copper in the fastener. Silicon Bronze is superior in corrosion resistance to 316 stainless steel; it is more expensive than most fasteners. Silicon bronze is used in marine environments, corrosive environments, high heat environments, and it is suitable for use in standard applications for aesthetic purposes. Often used in plumbing and electrical applications, silicon bronze fasteners are also found on tattoo machines and in power plants. Silicon bronze is similar in color to copper and is sometimes used in finish applications for the color.
Silicon Bronze Fasteners are made from alloy 651 Silicon Bronze
Brass is an alloy made of copper and zinc. The color of brass can vary from dark to light based on the zinc content; more zinc content produces lighter brass. Brass is prized for its corrosion resistance; however it is quite soft so it is not suitable for all applications. Brass conducts electricity and is also a good conductor of heat. It is often used in pipes, weather stripping, trim, radiators, musical instruments, and firearms.
Machined Brass Fasteners (Screws, nuts, bolts, etc.) are made from alloy 360 brass, and non-machined parts like washers are made from alloy 270 brass.
Aluminum is a common material that is very soft and lightweight. Aluminum alloy may be comprised of several materials including iron, manganese, silicon, copper, zinc and silicon. Aluminum rivets are among the most common aluminum fasteners.
Aluminum should never be used with Stainless Steel, galvanic corrosion may occur.
Alloy Steel is the most common material that fasteners are manufactured in. Alloy steel fasteners are often treated, coated or plated with zinc for additional corrosion resistance. Alloy steel is used for the hot dipped galvanized process, treated in a molten zinc bath which creates a tightly bonded alloy finish. Alloy steel is most often available in Grade A, Grade C, Grade 2, Grade 5 and Grade 8. Untreated alloy steel fasteners are black.
Titanium is extremely corrosion resistant with superior strength to weight when compared to aluminum. The tensile strength of titanium can reach or exceed 150,000 PSI. They work well in high temperature environments and is used largely by the aerospace industry. They are also used extensively in the chemical industry due to their strong resistance to corrosion and oxidizing chemicals.
Copper is used in very specific applications. They are highly conductive and corrosion resistant. They are often used for electrical and thermal industries. Fasteners in this variety are not magnetic and can only be hardened by cold-forming. Copper has the tensile strength of around 30,000 PSI.
Nickel works well in high and low temperature environments. Nickel fasteners are very strong, extra-ordinarily tough and ductile. Nickel is often used with other materials to create an even stronger fastener. Fasteners made of nickel-copper alloys have a tensile strength of roughly 80,000 PSI while fasteners made of nickel-copper-aluminum have a tensile strength of around 130,000 PSI. While fasteners with high nickel content offer excellent strength and corrosion/oxidization resistance but are typically not used consistently due to their high cost.
Bolt Head Markings: What do they mean?
Bolt Head Marking Meaning Transcript
Scroll Down To Continue Reading
Bob: Welcome back to Albany County Fasteners - Fasteners 101. I'm Bob and today we're gonna talk about markings on heads. I'm gonna teach you about the different markings and what they mean. So let's get started.
All right, I have a bunch of bolts here and I just wanted to go through the markings on these bolts so you understand them when you read them. Some of the markings on here will indicate that it's a grade 8, grade 5, grade 2, standard alloy, 316 stainless, or 18-8 stainless. So I'm gonna show you a couple of heads.
First, I'm going to show you this piece of paper here which basically shows you the standard markings, according to IFI requirements, and when you look at this you can see that some bolt's heads have absolutely no markings, some have strikes on them, and then some have like a number and a letter on it, like a b7.
Okay, so this here has no markings on it. Only marking that it does have is a manufacturer's marking. So how do you tell the difference? Typically, you'll see initials on there, this is an lb okay? That's a manufacturer's marking, whereas, if you took this one here, which has no markings, that would be a standard grade 2 bolt. Just for your information.
On this one we have three slashes and typically three slashes is going to be grade 5. You see the JH there? That's a manufacturer's marking. So you have two different types of marks here. You have a manufacturer's mark to them. So if someone questions this bolt, should it fail, the manufacturer knows right away when he looks at it if it's his bolt. The three slashes that you see on this head, that indicates that it's a grade 5 bolt.
This is a great 8 bolt. Again you see JDF on that bolt on the top. Those initials again are manufacturers marking to indicate that this is their bolt and then you see 1, 2, 3, 4, 5, 6 slashes indicating it's a grade 8. If it had no manufacturers marking, you would just see those six slashes and that would indicate to you that you have a grade eight bolt.
And the reason why you're looking for these? So when you buy bolts, you want to make sure that you have the correct bolt for your application. In cars, you don't want to use a grade two for certain applications such as, suspension, tying in your front arms, it's not made for that. You typically want to go for a grade 5 or a grade 8 depending on what the manufacturer recommends and that's, you know, just talking about different applications.
This bolt here which is a hot dip galvanized alloy bolt. It has, again, the manufacturers markings: the XYLX and then it says 307A. 307A is the indication of the strength of the bolt. Basically, this is equal to like a carriage bolt strength, a grade 2 or better, a little bit better than a grade 2, but standard alloy. These are not heat treated.
When you're dealing with grade 8, these are through-and-through heated bolts so they're treated for strength. Grade 5 are partially treated.
On to the next one, you can see a THE at the bottom. This is a stainless bolt. That's a manufacturer's mark and you will see here S30400. That's 304 stainless steel. That's what that's telling me. So when I read a stainless, stainless does not come with slashes. They come with an actual marking of the level of stainless. This one here you'll see the manufacturers marking ABF, I'm sorry, ABP and then you'll see S304. The S stands for stainless and the 30400 is the marking for stainless steel and those markings that you're seeing on these bolts are standard to IFI recommendations which are standardized throughout the industry.
This one here, this is an S316, so this is a higher grade stainless steel. You can see here that it says S-3-1-6-0-0 and at the bottom you see the manufacturers marking again THE. That's the manufacturer that made the bolt and the last one: this is 316 stainless. In this situation it also has another manufacturers marking on it: F-5-9-3-H. You can see that there, then it has like a logo punched into the head. That again, is a manufacturer's marking.
So there you go. I just wanted to show you how to read these things so you understand them. So when you're looking at them and a lot of you car guys want to grind these things off, but before you grind them off know what you bought, so you understand what's supposed to be in the box when you receive it.
Now that you know what type of material to use visit our Shop by Materials page to find what you need!
Want to learn more about Fasteners? Check out our Weekly Blog for new posts every Monday!