Stainless Steel & Aluminum: Why You Shouldn’t Use Them Together and Proper Precautions To Take If You Do

Why Can’t You Use Stainless Steel and Aluminum Together

Galvanic Corrosion

The combination of aluminum and stainless steel causes galvanic corrosion. In order to understand why you shouldn’t use stainless steel and aluminum together, we first need to understand how galvanic corrosion works. Galvanic corrosion is the transfer of electrons from one material (anode) to another (cathode). In addition to knowing what galvanic corrosion is, we also need to understand the technical terms that go along with it.

Here are all of the technical terms we will be using during this post:

Anode – material that is positively charged, electrons leave this material
Cathode – material that is negatively charged, electrons enter this material
Electrolyte – liquid that aids in the process of electron transfer
Corrosion/corrode – Destroy or weaken metal gradually

How It Works

Galvanic corrosion occurs when two materials (an anode and a cathode) come into contact with each other and an electrolyte. Electrolytes can be environmental factors such as humidity or rainwater. When these factors come into play, electron transfer will begin to occur. Depending on the level of resistance in an electrolyte, this transfer can happen much faster. This is why salt water, an electrolyte with a very low resistance, is a common factor when considering what product to use. Due to this, it is incredibly important to consider what material you are going to use in an environment. When working with a marine, salt water environment, you even need to consider the type of stainless steel you are using.

There are multiple kinds of rust that can occur during the oxidization process. To find out more about them please read this blog post about Three types of rust that frequently occur.

Our Example

For the rest of our post, instead of referring to anode and cathode, we will be using the example of aluminum (anode) and stainless steel (cathode). When aluminum and stainless steel are used in an assembly together, the electrons from the aluminum will begin to transfer into the stainless steel. This results in the aluminum weakening. This weakened aluminum causes it to deteriorate at a much faster rate. This can lead to an extended life of the stainless steel. Note: Aluminum, if left on its own with the electrolyte, will still lose its electrons eventually, but having stainless steel present will significantly speed up this process.

The galvanic corrosion practice is actually commonly used in plating to create a sacrificial layer on top of another material. Zinc plated steel and black oxide are commonly used examples.

Exceptions

Each and every assembly is situational. As metal relies on its environmental factors to corrode, and there may be places where you can use some metals together without seeing these effects. If the environment is very dry, sheltered from weather and dirt then you, may try using metals together. However, in most situations the environment is not temperature and humidity controlled, rust will occur. Due to this, Albany County Fasteners recommends never using aluminum and stainless steel together. We also recommend using metals exclusively for maximum life. Stainless with stainless, aluminum with aluminum, brass with brass. Mixing metals can affect the strength of the application, the lifespan of the fasteners, the corrosion of the materials, etc.

The other situation in which these materials can be used together with little impact on rust prevention is if the cathode area is very small when compared to the anode area. For example, if the base material is a large sheet of aluminum, then using very small stainless steel screws will not dramatically decrease the life. Conversely, if you use aluminum to attach a large sheet of stainless steel, the aluminum life will be dramatically shortened.

Albany County Fasteners recommends the use of neoprene EPDM or bonding washers in between stainless fasteners and aluminum materials, the neoprene forms a barrier in between the metals, preventing corrosion.

Environmental Factors To Determine

Many factors need to be considered when choosing the correct material for your installation.

Factor	Why It Matters
Duration of electrolyte contact	The longer an electrolyte is in contact with aluminum and stainless steel, the more likely there is to be a transfer of electrons.
Electrolyte Resistance	The lower the electrolyte resistance the easier it is for electron transfer to occur. Ex: salt water has a very low electrolyte resistance.
Stagnant Water	Water that sits and takes a very long time to dissipate can lead to extended exposure to electrolytes.
Dirt	Dirt (especially not in direct sunlight) can absorb an electrolyte and hold it for very long periods of time. This can result in increased exposure to the assembly if it is not kept clean.
Humidity/Fog	Both are environmental factors that lead to increased water in the air. If the environment is prone to these factors, the exposure to electrolytes is considered to be extended
Crevices	Crevices provide a catch for moisture (electrolyte) which can end up holding it against the materials for an extended period of time.

Noble Metals

If you decide that you need to use two different materials together, we recommend using an anode as the base material and making sure that it is significantly larger than the cathodes. Cathodes can also be called noble metals or metals that have a high resistance to oxidation (rust). We have compiled a list of noble metals below:

Gold
Iridium
Mercury
Osmium
Palladium
Platinum
Rhodium
Ruthenium
Silver

From Anode To Cathode

To mitigate the effects of galvanic corrosion even further, it is recommended to use materials that are less likely to cause electron transfer when exposed to each other and an electrolyte. The following list is a list of materials. *Note: the closer the two metals on this list, the less likely they will be to suffer from the negative effects of galvanic corrosion.

Magnesium
Magnesium Alloys
Zinc
Beryllium
Aluminum Alloys
Cadmium
Mild and Carbon Steel, Cast Iron
Chromium Steel (With Less Than Or Equal To 6% Chromium)
Active Stainless Steels (302, 310, 316, 410, 430)
Aluminum Bronze
Lead-Tin Solder
Tin
Active Nickel
Active Inconel
Brass
Bronze
Copper
Manganese Bronze
Silicon Bronze
Copper-Nickel Alloys
Lead
Monel
Silver Solder
Passive Nickel
Passive Inconel
Passive Stainless Steel (302, 310, 316, 410, 430)
Silver
Titanium
Zirconium
Gold
Platinum

How Can I Stop Galvanic Corrosion?

There are a few steps you can take if you MUST use these materials together.

Add an insulator between the two materials so they no longer connect. Without that connection, the transfer of electrons cannot occur. Well Nuts are a commonly used fastener to help separate materials that can suffer from galvanic corrosion.
Use materials with the same potential. Metals with the same corrosion resistance are typically ok to use together.
If you are in a situation where only one of the materials will come into contact with an electrolyte then transfer of electrons will not occur.
If there is a coating on the cathode it can prevent the transfer through increased resistance.
Consider your environment before installing. Choose materials that will work for your environment.
Coat or paint your assembly (completely) so that the electrolyte cannot make contact with the materials
Use neoprene EPDM or bonding washers as a barrier in between the metals.

If you’re curious about the types of materials we offer and more about them, check out our Materials Reference Guide.

Why Do Some Bolts Have Shoulders?

There are many different types of bolts available for use. From carriage bolts to hex cap screws, many of them can be seen sporting a shoulder (area near the head of the bolt without threading). But why? What does this area do?

Shoulder or Shank?

A shoulder or shank is a term that can be used to describe this unthreaded portion of a bolt. For different types of fasteners the appearance of a shank can mean different things. We made a post a while back about why would screws have a shank; Bolts have a shank for an entirely different reason though.

Bolt Shoulders

Bolt Shoulders exist for two reasons. The first is to create an area on the bolt where sheering is less likely to occur. If a load is pulling sideways against the unthreaded area of a bolt then the bolt will be less likely to snap as the areawhere the pressure is being placed is stronger than the threaded portion. The second reason for a shank is to allow for more versatile uses. This shank can act as an area for something attached to the bolt to be moved around.

Jobber Vs. Mechanics Drill Bits: The Difference Between Drill Bits

What Is The Difference Between A Jobber and Mechanic Drill Bit?

Jobber drill bits? Mechanics Drill bits? I JUST WANT TO DRILL A HOLE!!

Have you even felt frustrated at how much you have to learn to do something as simple as drill a hole? We feel the same way; that’s why we here at Albany County Fasteners have taken some time today to help you understand the difference between a jobber length and mechanics’ length drill bit so you can be sure to choose the right tool for your job.

Jobber Drill Bits

A jobber drill bit is a bit that has a long length compared to its diameter. Jobbers have a length anywhere from 8-12 or 9-14 (depending on who you ask) times the diameter. These bits can be measured using a number of different systems including a basic number range (1-80), letters (A-Z), wire (increase by whole number), standard metric sizing or in fractional sizes.

As far as fractional sizes are concerned, there are three different size increments used to measure jobber bits:

1/64 inch to 1 inch
1/16 inch to 3 inches
1/8 inch to 3 1/4 inches

Mechanics Drill Bits

The correct terminology is actually a mechanics length drill bit. A “mechanics drill bit” is actually a jobber drill bit. Did you get the joke?

A mechanics length drill bit is simply a bit with a shorter flute length and shorter overall length than a standard jobber bit. This shortening of the bit makes it considerably stronger and less prone to breakage and shearing, making it suitable for harder drilling.

When To Use Each…THE ANSWER!

Determining if you should use a jobber bit vs a mechanics length (jobber) bit, is actually quite simple. A regular jobber bit is best used in softer materials such as wood, composite, and soft metals. For harder materials and hard metal drilling, a mechanics length drill bit is recommended as they are a stronger bit. Jobber length drill bits are the most common and popular type of drill bits.

Figuring Out Drill Speeds: RPMs and Bit Life

What Speed Should I Drill At?

Rivet Removal 5

Figuring out RPM speed for your drill can be very confusing. Sure, there are recommended drilling speeds all over but they seem to vary from place to place. Instead of creating another chart for you with our recommendations, we want to actually teach you a bit about why we should drill at different speeds for different circumstances. Knowing this information, we can create a determining drill RPM best practice guide.

Drill Bits

The goal of most is to balance the life of a tool (drill bit) and the speed of the drilling(RPM) while not compromising the material. This is often how the optimal RPM is found.

We know that not everyone is looking for this cross point however, you may want to save money by burning through less drill bits or get a job done more quickly by speeding up the drilling pace. With the following considerations you will be able to determine what direction you need to move in to get the job done how you need it to.

Speed

The first thing to consider is speed (RPM’s) of a drill bit. When drilling into a harder material the general practice is to go slower. As the bit turns it begins biting or cutting into a material. This causes friction which will heat up the material and the drill bit. If the material begins to show signs of discoloration or smoke there is a good chance that the drill bit is creating too much friction which, in turn, will cause the material to overheat. This over-heating will result in a warped or damaged material and a quickly spent drill bit.

We can look at the graph to the right for a visual representation of how this effect works. As you can see when our RPM (speed) decreases the life of the bit will be extended. Most manufacturer recommendations will attempt to find the best compromise here while someone who recommends speeds to save drill bit life will obviously aim lower. We also recommend using drill bit lubrication for metal-cutting to extend the life of your drill bit.

Size

Another factor to consider is the size of the drill bit. A larger drill bit has far greater surface contact per revolution when compared to a smaller one. This means that a larger drill will generate more friction per revolution as well. So while it is perfectly fine to use a small bit at a higher RPM in a material, you may notice the larger bit causing some of those warning signs we talked about earlier. If this is the case, simply slow down and let the bit do the work.

Drill Bit Function

Different drill bits are specially designed to cut through different materials. This can be done either by altering the design of the bit itself, making it from a harder material, coating it or just adding a stronger tip to the bit to make the initial cuts. Making sure you have the proper bit for material is also incredibly important.

Material

Drill Bit

The other consideration you will need to factor in while drilling is the material you are drilling into. If you drill at the wrong speed your bit will cause the material to heat up and can actually change the properties of the material you are drilling into. You can also ruin materials this way such as burning wood.

Hardness

The hardness of a material is the consideration you should make when beginning to work on it. Different materials have different hardness and as a result, different temperaments to heat and drilling. Choosing the appropriate bit for the material can cut down on wasted bits and damaged materials.

Outcome?

So now that we know all of the different factors that should be considered when drilling, let’s come up with an order of operations for determining the best drill speed for you.

*Note: This is a very generalized overlook of how materials can react to different temperatures caused by friction.

Determining Drill Speed

Identify the material you are using.
Find the appropriate drill bit suited for your material.
Determine the size of the hole you need to drill into the material.
Decide what is more important: getting the job done faster or preserving the life of the drill bit.
Begin on a slow RPM setting and test out the bit.
ALWAYS (especially at high speeds) pay attention to the material.
If the bit is cutting fine and you desire a faster pace simply increase the RPM of the drill
Adjust as necessary.

Considerations

Watch for discoloration, smoke and bit chipping as these are all signs of drilling too quickly.
If it is your first time drilling into a material, always drill slowly and work your way up to the speed you want.
This method will take some practice to find comfortable ranges have fun with it do some experiments.
Keep a notebook on hand so you can record your findings and keep your own recommended drill speeds on hand.
- You can also record other information in this notebook such as which bit and size you used etc.

Power Drill Adjustable Slip Clutch / Torque Control

Power Drill Adjustable Slip Clutch / Torque Control Transcript

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Bob: Welcome back to Albany County Fasteners – Fasteners 101. I’m Bob and today I want to demonstrate to you a clutch that’s built into your drill.

Basically, you have a clutch on the head of your drill that goes anywhere from a number one up to, at least on mine, is a number 15. Okay, and then you have what they call drill mode and it has a little drill bit there so there’ll be no slippage.

So I want to show you so you don’t over-drill your product into your material. Now that could be into steel, it could be into to wood, or finish materials so you don’t dimple the wood. Right now, I have set this to a number ten on my drill. I’m going into a piece of 2×4 pine and once the screw starts to hit the face of the wood, the clutch in here will start to slip and I just want to demonstrate this to you.

I’m going to start it now and you get no resistance as far as driving it in but once it hit, the clutch slips and it stops the drilling. It doesn’t go any deeper into the wood.

Now if you wanted to drive that in less you would put the clutch at a number, let’s say number eight or number nine and then obviously the clutch will start to slip even more. However, as you’re driving if you would have set this to a number one then when you get about half way in the clutch is going to start to slip and you’re going to stop driving the screw in and you’re going to have to readjust the clutch.

That’s your quick tip for today. Thanks for watching.

Why Do Wood Screws Have A Shank?

It’s time to start your next wood working project. Grab your tools from the garage, find a box of screws, and wood, cut and ready to be installed. You start driving your first screw and boom, it stops and snaps. You try again, same thing. Then you realize you are using sheet metal screws, not wood screws! One quick trip to AlbanyCountyFasteners.com offers a quick fastener fix and your package shows up in the mail few days later filled with deck screws and wood screws. Hastily, you grab the package in excitement and run out to your shop to continue your work. Open the box and wait, what’s that? Why do these screws have an un-threaded portion? That can’t be right…Why would you want that?

It is one of the most misunderstood designs in the industry. Why is there a shank (shoulder) on a wood screw? If a wood screw was threaded all the way up, it would overheat and snap. Before we can explain why this happens, let’s start with the basics.

What Is A Wood Screw?

A wood screw is a screw made up of a head, shank and threaded body. Since the entire screw is not threaded, it is common to call these screws partially threaded (PT).

Head	The head of a screw is the portion that contains the drive and is considered the top of the screw. Most wood screws are Flat heads. Other common heads: Oval, Round, Hex, Modified Truss, Trim Flat.
Shank	The shank is the smooth portion of a wood screw which has no threads and begins immediately beneath the head.
Threaded Portion	The threads start just below the shank and extend all the way to the tip of the screw.

Now that we know what the different sections of a screw are, we can begin to understand what exactly happens during screw installation.

The unthreaded shank of a screw has dual purposes.

The First Purpose

First, when a screw that is fully threaded is driven into wood, this screw can connect two pieces of material together but it will not pull the two pieces against each other; once the head reaches the material, the screw will stop spinning.

Having an unthreaded shank at the top allows the tip of a wood screw to pull the screw into the wood just as a regular screw would. The difference is that the shoulder portion of the screw will actually slide through the first layer of wood and pull it against the head. This causes compression from the head to the threads. When installing two pieces of wood together then the first will be pulled tightly against the second one. The threads can continue to pull forward as long as enough torque is applied. Coincidentally, this can also make the removal process much easier than trying to remove a fully threaded screw.

*Note: This process of continuing to tighten after a wood screw reaches the head and snug wood together is known as over-tightening and may cause damage as the head is pulled to forcefully into the wood.

The Second Purpose

Second, when a fully threaded screw is being screwed into wood the screw threads cause friction. This friction results in the screw heating up. This causes two flaws in the material. As the metal heats up it will begin to expand. Once it expands inside of a hole that was drilled for a specific sized screw, the screw will seize in the hole. At the same time, the materials overall strength has now also been compromised due to the heat. Overheating leads to a screw breaking and snapping.

These two factors will highlight any flaws the screw may have and exploit them. This typically results in bending or snapping of the screw. So, how can a shank help? The shank allows for heat dispersion in a screw. As the threads begin creating heat, it moves up into the shank which will take longer to heat up and will not generate nearly the same amount of friction when it goes through the wood.

This unthreaded shoulder will minimize the amount of heat a screw generates upon install thus keeping it from expanding in size and compromising the materials strength.

Conclusion

To conclude, the shank of a wood screw is used to tightly compress two pieces of wood against each other and minimize the heating up of the screw caused by friction. This results in a strong firm hold between two wooden materials with little effort, and just as importantly, no broken screws.

Other information

Looking for more information about screws? Check out our Screws blog post to learn about many different types of screws.

We also recommend using lubrication when installing wood screws into very hard wood. A DIY option that is available is simply adding soap to the fastener. Soap acts as a natural lubricant but it should be noted that many soaps have glycerin in them which can actually attract moisture. This can result in fasteners deteriorating faster than expected.

A full blown solution is to use MRO Anti-Seize Solution. Not only will this lubricate your nails before installation but it can also add a protective coating to deter from corrosion!