The meaning of the term "structural fastener" is somewhat ambiguous. Here's what it used to mean:
As recently as a January 2020 article by ITA Fasteners, structural fasteners are described as being, "… characterized by strong, heavy-duty materials that facilitate the construction of structures employing steel to steel connections. They are an ideal choice … for connecting one metal structure to another."
While not inaccurate, according to Steave Klein, National Sales Manager for Fasteners at Austin Hardware®, "That phrasing comes from a time when steel was the strongest material available for construction and structural applications. In the modern world of today, while steel is still commonly used in all types of manufacturing, we also have many other materials, some of which are stronger than steel, and due to some of their other characteristics, better suited to certain load-bearing applications."
This definition also limits structural fasteners to their use in applications such as beams and girders in bridges, buildings, and any other heavy construction projects where two steel objects need to be fastened together.
The majority of these structural fasteners are composed of quenched or tempered steel and have a minimum tensile strength of 120 ksi for use in structural connections. Examples include ASTM A325 and A490, Types 1 and 3 structural hex bolts, A563 heavy hex nuts, and F436 flat washers that are designed to work together.
There are, however, other types of fasteners that fall into the category of "structural" as well. Two readily available types are Structural Blind Fasteners and two-piece structural fasteners.
Structural blind fasteners include high strength rivets and blind bolts. Two-piece structural fasteners are typically known as lockbolts. They're all designed for durability and vibration resistance and are commonly used in commercial vehicle and trailer manufacturing, as well as the automotive, bus and rail, and HVAC industries, among others.
Structural blind fasteners are ideally suited for structures where access is limited to one side. With higher shear and tensile strengths than standard blind rivets, they offer all the benefits of standard rivets, with the necessary added strength.
So, where do structural blind rivets get their strength? The internal locking mechanism of a structural blind rivet or blind bolt retains the mandrel (pin) within the shear plane of the rivet body after installation, resulting in a much stronger structural fastener than a standard open-end blind rivet. The thickness, strength, and material of the substrates to be fastened drive the specific type of blind structural rivet or blind bolt you will need.
A lockbolt is a two-piece engineered fastener system consisting of a pin and a collar. They offer high shear and tensile strength while also being designed to withstand intense vibration in a wide range of applications. They are permanent, mechanically locked fasteners that, unlike conventional nuts and bolts, won't loosen, even under the most extreme vibration.
Lockbolts achieve their vibration resistance by literally cold-forming the collar into the grooves located on the body of the pin during installation. An added benefit is that washers are not necessary when using lockbolts. This is because most types of lockbolts offer flanged collars and head configurations that don't require washers. As a non-torqueing fastener, lockbolts provide clamping action, not rotation, upon installation.
Austin Hardware® is an authorized distributor of structural blind fasteners for Huck and other major fastener manufacturers. Steave Klein has over 30 years of experience in the fastener business, including product management for one of the world's best-known manufacturers of structural blind fasteners and lockbolts. Steave's a valuable resource for anyone requiring these products. If you have questions about the right type of structural fastener to choose for your application, we encourage you to contact Steave.
