Fasteners are manufactured in a wide range of materials from common steel to titanium, plastic and other exotic materials. Many materials are further separated into different grades to describe specific alloy mixtures, hardening processes, etc. In addition, some materials are available with a variety of coatings or platings to enhance the corrosion resistance or alter the appearance of the fastener.
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Fastener material can be important when choosing a fastener due to differences between materials in strength, brittleness, corrosion resistance, galvanic corrosion properties and, of course, cost.
When replacing fasteners, it is generally best to match what you are replacing. Replacing a bolt with a stronger one is not always safe. Harder bolts tend to be more brittle and may fail in specific applications. Also some equipment is designed so that the bolts will fail before more expensive or critical items are damaged. In some environments, such as salt water, galvanic corrosion must also be considered if changing fastener materials. For more information see our About Galvanic Corrosion page.
Stainless steel is an alloy of low carbon steel and chromium for enhanced corrosion characteristics. Stainless steel is highly corrosion resistant for the price. Because the anti-corrosive properties are inherent to the metal, it will not lose this resistance if scratched during installation or use.
It is a common misconception that stainless steel is stronger than regular steel. In fact, due to their low carbon content, many stainless steel alloys cannot be hardened through heat treatment. Therefore, when compared to regular steel, the stainless alloys used in bolts are slightly stronger than an un-hardened (grade 2) steel but significantly weaker than hardened steel fasteners. Unless great care is taken, stainless fasteners are susceptible to seizing up during installation , a phenomenon known as galling.
Most stainless steel fasteners are much less magnetic than regular steel fasteners though some grades will be slightly magnetic.
18-8 refers to any stainless steel containing approximately 18% chromium and 8% nickel. This is the most common stainless designation for hardware. For information on 18-8 stainless steel material properties see our Material Grade Identification and Properties Chart .
A highly corrosion resistant grade of stainless steel. Ideal in salt water and chlorine environments. More expensive than 18-8.
A stainless alloy that is harder than 18-8 stainless steel, but not as resistant to corrosion.
Steel is the most common fastener material. Steel fasteners are available plain as well as with various surface treatments such as zinc plating, galvanization, and chrome plating.
Steel fasteners are commonly available in 4 grades: Grade 2, Grade 5, Grade 8, and Alloy Steel. Many other grades exist but are used far less often. Grade 2, 5, and 8 are usually plated with a slightly blue-ish or yellow zinc coating, or are galvanized, to resist corrosion.
Bolts are typically marked on the head to show what grade bolt they are. For a list of the most common grade markings see our Material Grade Identification and Properties Chart . Note that, in addition to the grade marking, many bolts also have a manufacturer's mark.
Grade 2 is a standard hardware grade steel. This is the most common grade of steel fastener and is the least expensive. Except a possible manufacturer's mark, Grade 2 bolts have no head marking.
Grade 5 bolts are hardened to increase strength and are the most common bolts found in automotive applications. Grade 5 bolts have 3 evenly spaced radial lines on the head.
Grade F is roughly equivalent to Grade 5. Grade F nuts are used with Grade 5 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.
Grade G is roughly equivalent to Grade 8. Grade G nuts are used with Grade 8 bolts.
Alloy steel bolts are made from a high strength steel alloy and are further heat treated. Alloy steel bolts are typically not plated, resulting in a dull black finish. Alloy steel bolts are extremely strong but very brittle.
Silicon bronze, often referred to simply as bronze, is an alloy made mostly of copper and tin with a small amount of silicon. Bronze is used primarily in marine environments. It is preferred over stainless in wooden boat construction and re-fastening due to its superior corrosion resistance, and over brass due to its higher strength. Bronze is similar to copper in color and is also sometimes seen in fine woodworking where it is used for its appearance. The main drawback of bronze is its high cost.
Brass is an alloy of primarily copper and zinc. Brass is highly corrosion resistant and electrically conductive. However, its use as a fastener is somewhat limited due to its relative softness. It is used primarily for its appearance.
Aluminum is a light, soft, corrosion resistant metal. Like stainless steel, aluminum's corrosion resistance is inherent to the material. Therefore, scratches and nicks will not effect the corrosion resistance.
Fasteners are made from a variety of aluminum alloys, with elements such as manganese, silicon, iron, magnesium, zinc, copper, and silicon being added to increase strength and melting point.
Rivets are often made from aluminum alloys in the -series, which uses magnesium as the primary alloying element.
Many steel fasteners are electroplated with zinc for better corrosion resistance. Fasteners that have been zinc plated have a shiny, silvery or golden appearance, referred to as clear or yellow zinc respectively. They are fairly corrosion resistant but will rust if the coating is destroyed or if exposed to a marine environment.
Galvanizing is another coating involving the application of
a layer of zinc. Hot dip galvanizing puts the thickest
possible coating on the metal, resulting in superior corrosion
resistance. Due to the thickness of the coating hot dipped
galvanized bolts are not compatible with other nuts. Galvanized
nuts are tapped slightly larger than other nuts to accommodate
this coating.
Hot dipped galvanized fasteners are frequently used outdoors, especially in coastal
environments.
Fasteners are chrome plated and polished for appearance. Chrome plating provides similar corrosion resistance to zinc plating. The main drawback of polished chrome is its high cost. If more corrosion resistance is required, stainless steel may be chrome plated, preventing any corrosion should the chrome be penetrated.
By Marcy Marro Fasteners are an essential piece of any metal building project. From the framing to the metal wall and roof panels, fasteners are necessary to put any metal building together. With fasteners being such an important aspect of any project, it is also important to make sure that you are using the correct&#; Continue reading
Choosing the Right Fastener: What you need to know about metal wall panel fasteners
Fasteners are an essential piece of any metal building project. From the framing to the metal wall and roof panels, fasteners are necessary to put any metal building together. With fasteners being such an important aspect of any project, it is also important to make sure that you are using the correct type of fastener for each piece of the building, since when improper screws are used, both the fastener and the panel system can fail.
When selecting fasteners for metal wall panels, Joe Stager, vice president of product development and marketing at Cleveland, Ohio-based Triangle Fastener Corp., says that the most important thing is to do is use a fastener that is specified by the panel manufacturer. &#;If none is specified, select a screw that is designed for attaching into the thickness of the girt and long enough to allow at least three full threads to extend beyond the girt.&#;
Keith Self, product manager at Birmingham Fastener Inc., Birmingham, Ala., adds that since a fastener is only a small part of a larger system, it is only going to be as strong as the material it is fastening. &#;Many factors determine which fastener is best suited to your specific application. Although several different fasteners may work for the application, some will perform better in each circumstance. Material substrates, gauges of materials, even where a particular building is being erected can determine proper fastener selection.&#;
Structurally, there are four critical factors that should be considered when selecting a fastener, explains Tom Hulsey, director, technical services and applications engineering at SEALTITE Building Fasteners, Tyler, Texas. They are:
In addition to the above factors, there are a number of aspects of fasteners that contractors should keep in mind when selecting the right ones for installing metal wall panels.
Contact us to discuss your requirements of Metal Fasteners Supplier. Our experienced sales team can help you identify the options that best suit your needs.
What material a fastener is made up of is an important consideration. Hulsey notes that while material selection is based upon the function and the expected long-term performance of the fastener, Self adds that factors involving dissimilar metals and galvanic reaction must be considered, including how the fastener will react with its environment, as well as the materials it is being used to attach.
&#;Generally speaking, the industry uses carbon steel fasteners due to their cost effectiveness and performance ability,&#; says Eric Velliquette, vice president of sales and marketing, Atlas Fasteners, Ashland, Ohio. &#;Carbon steel is a harder material that enables the ability to manufacture fasteners with a drill point.&#;
&#;Most self-tapping screws used to attach metal wall panels are made of c-c carbon steel,&#; says Stager. &#;These screws are case-hardened so that the surface of the screw is hard enough to tap the steel sheet and girt without stripping. There are also special &#;ductile&#; tapping screws that are produced from alloy steel like c that will bend without fracturing. They are designed for applications where excessive expansion/contraction or vibration is a concern and may cause a standard case-harden screw to fracture.&#;
Velliquette notes that 300 series stainless steel comes in a variety of grades and has great corrosion resistant properties, making it the material of choice when looking for a fastener with high ductility properties. Additionally, he adds that 410ss are used for customers who like the corrosion properties of the 300ss, but like the ability to have a fastener with a drill point.
For metal wall fasteners, there are two main head shapes-pancake and hex head. Hex head (external drive) screws provide the best installation stability compared to pancake head (recess drive) screws, according to Stager. Hex head fasteners are used for exposed fastener applications and concealed fastener panels when clearance is not an issue, he notes. Stager adds that pancake head screws are primarily used in concealed fastener panels where there is limited space in the joint of the panel, in addition to exposed applications when a low profile screw head is more aesthetically pleasing. While pancake head fasteners have a recessed configuration in the head for installation, Hulsey notes that hex head fasteners have a recess under the flange of the head to capture a sealing washer. &#;The hex shape allows for a more positive configuration to drive the fastener without damaging the surface finish,&#; he says.
&#;For light trim applications, a pancake head fastener works well,&#; notes Velliquette. &#;When you need a fastener for thicker applications, hex head fasteners work great due to higher drive torque requirements.&#;
Self adds that pancake head fasteners are limited to certain lengths and diameters, while hex heads are limited on sizes and drill abilities.
Fasteners are measured from underneath the head to the tip of the fastener, and the necessary length required is determined by the total thickness of the components being assembled. &#;The length of the fastener is best described as being the sum of the unthreaded drill point length, the length of the threaded body, and any unthreaded shank directly under the bearing surface of the head,&#; explains Hulsey. &#;The thread length should provide for full diameter threads to be engaged in the girt and at least two full threads to project through the girt when the fastener head (or sealing washer) is correctly seated against the wall panel and the assembly is correctly tightened.&#;
Stager notes that by having at least three full threads that extend beyond the material that is being tapped by the threads will allow the threads to tap the girt enough to produce acceptable pull-out and clamping loads.
Fasteners come in to styles: self-drilling or self-tapping. Stager notes that the main advantage of self-drilling screws is the ability to drill and tap the material in one operation, eliminating the need to pre-drill the materials, while self-tapping screws provide a fast and inexpensive alternative to drill-screws and typically produce higher strip-out loads when attaching to thin steel 20-gauge or less. Hulsey adds that self-tapping fasteners are manufactured without the drill point feature and require pre-drilling the girt with the proper sized drill bit for the diameter of the fastener being used.
&#;Erectors of wall and roof panels on steel-framed buildings generally use self-drilling fasteners,&#; says Hulsey. &#;Self-drilling points are sized to provide the correct hole diameter and point length for a specific range of girt thickness for a specific fastener diameter and thread type. When the thickness of the structural girt becomes significantly greater, a larger point diameter is needed in order for the following threads to properly engage the structural member without breaking the fastener.&#;
Velliquette explains that self-drillers have five different sizes ranging from #1 through #5 point, while self-tappers have three point types that include Type A, AB and B. &#;Whether it is a self-driller or self-tapper, each point has its own characteristics which make it superior for its proper application.&#;
Self-tapping screws
&#;Gimlet point and drill-point screws are capable of piercing and tapping steel,&#; explains Stager. &#;Gimlet point (sharp pointed) screws can pierce up to 20-gauge steel. Drill-point screws can drill and tap up to 1/2-inch-thick steel. Some points like Type BP are designed to assist the installer in positioning the screw into a &#;blind hole&#; so that the thread taps successfully.&#;
Washers play an important role in a building&#;s weather tightness, preventing leaks and adding in back-out resistance. Velliquette notes that it is important to choose a fastener with a non-conductive rubber washer. &#;The washer of a fastener becomes a barrier between two dissimilar metals,&#; he says. &#;When moisture is present, along with conductive washers, electrolysis begins to take place creating enhanced corrosion.&#;
&#;Washers are primarily composed of either EPDM rubber or neoprene rubber,&#; Self says, &#;with EPDM having a higher melting point and is more UV stable.&#; Other considerations are the difference between a &#;bonded washer&#; (metal-backed washer), and the &#;flange washer&#; design. The flange is part of the fastener&#;s head and has a loose EPDM washer, he adds.
Stager recommends choosing a bonded sealing washer that uses non-conducted EPDM sealant that has been vulcanized, and not glued, to the metal backing. &#;This will provide the optimal seal and minimize galvanic corrosion between the washer and the panel.&#; He continues, saying that for undercut head screws, make sure the washer is made of non-conductive EPDM material as well. &#;Be aware that the diameter of the washer provides a bearing surface against the panel that effects the pull-over strength of the panel over the screw and washer assembly. For optimal sealing capabilities, tighten the screw until the EPDM extrudes to the edge of the screw&#;s washer face.&#;
The purpose of coatings is to protect the fastener from the corrosive effects of the environment, while improving the aesthetics of the installed assembly, explains Hulsey. &#;Coatings on fasteners provide not only protection against corrosion but can also provide lubricity to allow the thread to tap the girt with acceptable torque,&#; Stager adds. &#;When corrosion of the fastener occurs, it can cause the fastener to fail due to stress corrosion cracking or other forms for corrosion induced fastener failure. It is recommended that any exposed fasteners be plated and coated with superior finishes that minimize corrosion.&#;
&#;Depending on environment and application, coatings are vital to the overall success of the attachment,&#; says Self. &#;Any fastener exposed to the elements needs to meet the requirements of the panel manufacturer, normally the tests consist of a salt spray test (ASTM B117) and a Kesternich test (DIN ), both tests compare the resistance to corrosion.&#;
Hulsey notes that carbon steel fasteners must be coated to protect them from red rusting. While the most common means of protection is zinc plating, painting or applying powder coating can provide additional protection. For stainless steel fasteners, Hulsey notes they are generally coated for color matching the panel, since corrosion resistance is generally not an issue.
When choosing fasteners for metal wall panels, Hulsey notes that contractors should be looking for a fastener that will provide the structural strength necessary to satisfy the building specifications and meet all applicable code requirements. &#;Performance properties that are important to the contractor are drill performance, sealing characteristics, long-term corrosion resistance and ease of installation.&#;
&#;Contractors should primarily be looking at what the application consists of, and what job the fastener will perform to determine the best way to achieve the desired results,&#; Self says. &#;Some factors to consider are pull-out, pull-over, tension strength and shear strength. Proper safety factors should always be used in all applications.&#;
&#;A fastener that has both superior corrosion resistance and consistent drill performance will save the contractor money, creating increased profitability,&#; adds Velliquette.
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