Frequently Asked Questions

In 2015, the ASTM consolidated the standards for structural bolts into F3125. Prior to the change, there were separate standards for high strength bolts including A325, A325M, A490, A490M, F1852 and F2280. 

Because these all fall under the high-strength structural bolting umbrella, these were changed to grades under the F3125 standard. Therefore, the newer standard of F3125 includes both heavy hex structural bolts and “twist-off” tension control structural bolting assemblies (including the nut and washer). 

In addition to the standard consolidation, certain technical aspects of the fasteners were also updated. Minimum tensile strength is now separated into a 120 ksi strength class and a 150 ksi strength class across the standard, and tension control bolts now have a maximum 1-1/4” diameter than the previous 1-1/8” diameter.

ASTM F3125 Grade A325 bolts and A490 bolts are two of the main types of structural bolts we sell, and they are the two you will most often see on a jobsite. The difference in grades A325 and A490 may seem simple. A490 is stronger than A325. That said, plenty of projects call for A325 bolts.

In a lot of ways, grades A325 and A490 are similar. Both of these F3125 bolts have a heavy hex head configuration, which gives a larger bearing surface to distribute the load. These structural bolts have a specific thread length and shank length. 

In structural bolting applications, this allows the bolt’s threads to not be in the shear plane (where the two plates meet up). The threaded section of the bolt is the weakest, thus a longer shank length makes for a stronger tensile connection. 

While these similarities make these grades of bolts seemingly identical, some fundamental differences make grades A325 and A490 different.

The two types of coating on ASTM F3125 Grade A325 bolting assemblies are hot-dip galvanized and mechanical galvanized (uncoated is also available). Though they may sound similar, they are very different coatings. It is against ASTM standards to mix the two coatings on a single bolting component.

Because hot-dip galvanizing produces a thicker coating than mechanical galvanizing, over-tapping the nut is necessary to accommodate the coating’s thickness. To over-tap a nut, the manufacturer increases the nut’s threads slightly for the nut to slide onto the bolt easily.

Because of this over-tapping of a hot-dip nut, a mechanical galvanized nut would not fit onto a hot-dip galvanized bolt. Also, a hot-dipped nut would be too loose for a mechanical galvanized bolt, as there is not enough thread engagement. This would also increase the torque required to tighten the fastener, and because the threads aren’t properly engaged, you could end up with a bolt assembly that is torqued but not properly tensioned.

Misaligned anchor bolts can be a major headache. Many industries use anchor bolts to attach structural elements, commonly steel, to concrete to ensure stability. One end is embedded into concrete, while the other is attached to the steel structure. 

Anchor bolt installation requires accuracy, but sometimes anchor bolts are misaligned during installation. This problem can be extremely difficult to fix, but the question remains: can you fix a misaligned anchor bolt?

As with most complex questions, the answer isn’t a simple yes or no. There are many questions to consider when determining whether a misaligned anchor bolt can be fixed, the most important being – have you consulted your land surveyor and engineer?

Every now and again, we get questions on structural bolt reuse, and the answer is always the same: maybe. When we talk about reusing a bolt, we’re referring to when a pretensioned bolt is loosened and then re-pretensioned.

Sometimes, you may need to remove a pretensioned bolt and then need to reinstall it. Depending on the type of bolt, and the express permission from your engineer, you may be able to reinstall it. RCSC Section 2.3.3 allows uncoated F3125 Grade A325 bolts to be reused with the engineer’s permission. Galvanized bolts and F3125 Grade A490 bolts that have been pretensioned may not be reused at all.

Snugging a bolt refers to tightening a bolt with a few impacts of an impact wrench or with the full effort of a worker using an ordinary wrench. F3125 Grade A325 bolts that are snugged can usually be reused. Snugged F3125 Grade A490 bolts and galvanized Grade A325 bolts can only be considered for reuse if snugged by hand or very lightly snugged with an impact wrench.

When we’re talking about structural bolts, particularly ASTM F3125 Grades A325 and A490, there are two types of structural steel: Type 1 and Type 3. On the outside, they look the same, but there’s one key difference: Type 3 structural steel is designed to weather, or rust, as a means of protection. Type 1 bolts can be galvanized to protect the bolts from corrosion. 

According to the RCSC, Type 1 covers medium carbon steel for F3125 Grade A325 bolts and alloy steel for F3125 Grade A490 bolts. Type 1 Grade A325 bolts can be mechanically coated or hot-dip galvanized to protect them from corrosion.

Type 1 Grade A490 bolts on the other hand are only approved for F1136 Grade 3 and F2833 Grade 1 coatings per ASTM F3125 and the IFI 144 standard. Unlike Type 3 weathering steel, any rust on Type 1 bolts will not act as a protective coating to the bolt.

Often, our customers will ask us to discuss torque values in regards to pretensioning structural bolts. Birmingham Fastener makes it a point to educate our customers on the difference between torque vs. tension and the importance of measuring the tension of structural bolts instead of just relying on torque.

Torque is often associated with installation, tightening, or inspection of structural bolts. Bolts are tightened in order to achieve tension – torque is only a by-product of this relationship to reach proper tension. Torque can vary greatly in this relationship to reach the desired tension, therefore, Birmingham Fastener stresses that you focus on tension first and foremost.

Structural bolting components, whether uncoated or galvanized, are lubricated for installation purposes. Sometimes it is necessary to reapply bolt lubricant. Though the types of structural bolt lubricant vary, both have a chance of coming off prior to installation. This is typically caused by exposure to the elements from improper jobsite storage. Reapplication of the lubricant is typically required prior to installation.

While there are no specific ASTM requirements that uncoated bolting assemblies be lubricated, their lubricant comes from the left over water-soluble oil from production. This oil ensures ease of installation. The lubricant can wash away when exposed to condensation, or it can evaporate when their containers are left open. If this happens, the assemblies can be difficult to install, and the bolt’s ductility is lessened due to the stress of tightening the non-lubricated bolt.

White rust is a common problem in the structural steel industry. It is typically caused by improper jobsite storage and a lack of air circulation. Aside from it harming the physical appearance of the bolt, white rust can break down the layer of protective coating on the bolt.

Many structural bolts are galvanized for their protection and durability. This galvanized coating is made of zinc, which is one of the best ways to prevent corrosion on steel. White rust is made up of zinc hydroxide, which is formed when zinc reacts with water and air. 

Zinc hydroxide is unstable and consumes the protective zinc coating. This typically happens when fasteners are “nested” together (packed flat one on top of another) and water gets in between the fasteners. It looks like white powder covering the surface of the coating (see image below). 

Fortunately, there are a few simple ways to prevent white rust from forming on your structural bolting components.

Self-tapping and self-drilling screws are two types of screws used in metal building and general construction, as well as many other applications and industries. Contrary to popular belief, the two terms are not interchangeable.

No construction project is ever completed without complication. Weather, material delays and human error all cause interruptions. Some delays can be avoided, however.  Simply ensuring you have the right tools for the job goes a long way in meeting your deadlines. 

Sometimes our customers ask for self-tapping screws when they actually want self-drilling screws, or vice versa. We don’t want you to waste time or money by ordering the wrong products.

Anyone serious about getting a job done efficiently and effectively needs to know the difference between self-drilling and self-tapping screws.

It’s important to achieve the proper tension when installing structural bolts. Fortunately, special structural bolting components on the market can make it easier to ensure proper torque and tension. 

Tension control (TC) bolts come built with a spline that pops off when the nut is properly torqued. For hex bolts, DTI washers can be just as helpful in displaying the proper tension. 

Two of the four methods of installing structural bolts cover tension control (twist-off type bolts) and DTI washers, respectively. Regardless of what you use, remember that bolts are tightened in order to achieve tension – torque is only a by-product of this relationship to reach proper tension.

There are two types of threads on mechanical fasteners: rolled thread and cut thread. Sometimes our customers ask about the threading process – particularly which type of bolt threading is stronger. Though both processes yield similar results, there are a few differences in each process that cause differences in the products.

The process of roll threading a bolt is a cold forming process using a set of hardened steel dies to form threads onto a bolt. The die protrudes into the outside diameter of the blank bolt to form threads onto the bolt. As the bolt is under high pressure, the steel grain flows in multiple directions, causing the bolt to be stronger.

Cut threading bolts involves severing the steel’s grain structure to produce threads. While rolled thread bolts offer some advantage over cut thread bolts in regards to strength and cost, cut threads can be manufactured to virtually all specifications, including larger diameter bolts. 

A lot can go into choosing a finish for your stainless steel fasteners. The two finishing operations most industries specify for their parts are electropolishing and passivation. 

Electropolishing is a chemical process that can be performed on almost all metal to remove imperfections and contaminants on the surface of the metal. The process involves submerging the fastener or other metal product in a temperature-controlled chemical bath. A current is then passed through the bath, oxidizing the surface and causing it to shed and deburr the contaminants and smooth out any flaws.

Like electropolishing, passivation is also a chemical process designed to remove imperfections from steel and provide a clean finish. In contrast to electropolishing, passivation does not produce a bright or shiny finish. Passivation is designed to improve corrosion resistance on stainless steel. Passivation is effective on most grades of stainless steel, but it is not recommended for certain types of alloys.

Proper jobsite storage and handling of structural bolting components can mean the difference between an organized, timely project and having to buy completely new bolting components – costing your team time and money. At Birmingham Fastener, we take jobsite storage seriously.

Most jobs require lot traceability for fastener storage. Lot traceability entails having production lot numbers on each container of nuts, bolts and washers. Each type of structural bolting component must be stored separately by lot. 

This level of organization ensures that the correct fastening components are installed in each portion of the job. It is also required for pre-installation verification testing. Though some jobs do not require lot traceability, we highly recommend it for all jobs, due to the level of organization it provides.

At Birmingham Fastener, we pride ourselves in being ISO 9001:2015 certified at our headquarters, our distribution center in Hanceville and our aerospace division in Huntsville. The ISO 9001:2015 standard lays out the criteria for a company to establish a quality management system. It is used by over one million companies across the globe. 

There are several different types of documents in the ISO 9000 family outlining standards, but ISO 9001 is the only one in the series requiring certification. ISO 9001 is a company or organization-wide standard that ensures companies are meeting their customers’ requirements for quality of products or services.

ISO 9001 can improve a facility’s standards, performance and overall quality of products. A properly functioning quality management system utilizes policies, procedures, work instructions and forms to properly document and define the processes involved in product realization. Organizations use this standard to demonstrate their consistency in manufacturing, building or developing their products.

As technology continues to grow and products evolve, we all look for ways to increase productivity and streamline the workflow – tools and fasteners are no exception. However, as lithium ion cordless tools and cordless impact tools become cheaper and stronger, some people believe these tools will increase productivity and make the job quicker and easier. 

Although these tools are very versatile, they are not designed for self-drilling screws. Every metal building screw manufacturer recommends 2000 RPMs or less on self-drilling screws and 900 RPMs or less for stainless steel fasteners.

For most metal building projects, a screw gun, or “tek” gun with an adjustable clutch and a depth sensing nosepiece is recommended. Although it is slower, it will increase productivity. By using a faster and stronger tool, like the cordless impact tool, you are introducing stress to the fastener. Adding stress to the fastener can be dangerous, therefore proper installation is paramount.

Hot heading and cold heading are the two ways to form the head of a bolt. Each process has its own advantages, though there are a few important considerations to make when choosing one over another.

At Birmingham Fastener, hot headed bolts generally range from 3/8” diameter to 2” diameter. Any material grade we supply can be hot headed, including stainless steel. The process of hot heading a bolt involves heating round bar in a furnace, then forming the head of the bolt in a header (like a die form). 

Birmingham Fastener cold heads bolts ranging in size from ½” diameter to 1 1/8” diameter. Most material grades we supply can be cold headed. As its name suggests, cold head forming is performed at room temperature. The round bar is shaped into a head by being squeezed between two die forms. The cold heading process allows for very tight dimensional specification to be achieved.