What to know before selecting fasteners

by David Flaherty | 7 January 2025 1:53 pm

In the construction industry, contractors need to get the right product for their applications. One thing that is often taken for granted in the industry is getting the correct fasteners.

Fasteners are less than 1 percent of the job cost but can wind up being 95 percent of the headaches. These headaches can come from giving the customer what they ask for and not what is really needed. Being asked the proper questions by fastening experts can give contractors 95 percent fewer headaches on their jobs.

Which fastener fits which material

Assessing what fastener best suits an application involves so many questions. For starters, what is the substrate? Knowing whether it is wood, concrete, steel, or some other material will determine which style of fastener point and threading is best.

A steel substrate can be one of the trickiest substrates to fasten into. With the invention of the self-drilling screw, pre-drilling is mostly a thing of the past; and now, with further innovations, pre-drilling is eliminated for up to 16-mm (0.625-in.) thick steel. Knowing the gauge/thickness of the steel is critical when assessing the necessary type of self-drilling screw—from a T-1 tip for light gauge steel, a T-2 and T-3 for medium gauge steel up to 6.3 mm (0.25-in) to a T-4 and T-5 for heavy steel up to 12.7 mm (0.5 in.) thickness. Proper tools with appropriate torque and RPM will maximize the fastener’s performance.

Important questions

Once the base material and necessary fastener type are confirmed, the next important factor to evaluate is the exact application. What is being attached to what? Are there multiple layers? Is there insulation (blanket or ridged)? And are there any spaces or standoffs in the assembly? The answers to these questions will determine the fastener length needed. When fastening into steel, at least two full threads of the screw must penetrate through the back of the material for maximum strength. If there is insulation or a void between the face and the base steel, an interior or exterior insulation screw with a thread void in the fastener shank will be ideal. The thread-void allows the screw to rotate while drilling the base steel, preventing the panel from riding up the threads, which would otherwise cause unsightly, unrepairable face puckering due to the jacking.

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If there is aluminum in the assembly, the fastener in contact with the aluminum needs to be 300-series stainless steel. These fasteners are very specialized and crucial to the proper installation. Specialty bi-metal screws, which comprise a stainless head and shank with a carbon steel tip, can drill and tap steel while ultimately ensuring only the stainless portion of the screw maintains contact with the aluminum. This is critical for avoiding failure due to electrolysis or hydrogen embrittlement. There are also all 300-series stainless steel screws for drilling and fastening aluminum to aluminum.

When the proper screw type is picked out, the last hurdle to jump is the head style and coating. Is the fastener going to be concealed? Does the head need to be low-profile or a pancake head to sit in a special clip or can it be a hex or pan head? Is an extra wide washer-face required for bearing area? If the fastener is exposed to the elements, is a bonded sealing washer required to prevent water infiltration? Then finally, what coating or plating is needed? An electro-plated fastener will give it a shiny and polished look but also lessen its corrosion resistance once installed. The most popular finish for today’s fasteners has quickly migrated almost exclusively toward the long-life coated outer finish. This coating will prevent the rusting and streaking of the panels while also withstanding the freeze-thaw climate of the Minnesota tundra and the rain and scorching heat of the Texas summers—and years later, it still looks like they were just installed. A minimum of “1,000 hour rated” coating is highly recommended.

This is a lot of information to take in. Whether you are a contractor, an engineer, or an architect, addressing these questions before you go out to the field will make the installation go as smoothly as possible and prevent those wasted hours and costly callbacks. This is why fastening experts are readily available to ensure we ask the right questions to make sure you get the right product.

Source URL: https://www.metalconstructionnews.com/articles/selecting-fasteners/

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