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The right one for the job: Drill through the differences among stainless-steel fasteners

Stainless-steel fasteners are known for their strength, durability and corrosion resistance. However, not all stainless-steel fasteners are alike -there are different grades, sizes and head styles. It's important to select and install the right fastener for the job, but knowing what type of stainlesssteel fastener to use isn't always easy given the vast number of fasteners from which to choose. To help you navigate through the selection process, let's take a look at some of the most typical types of applications and recommended fastener solutions.

Wood-to-Steel Framing

Grade-410 stainless-steel fasteners are ideal for attaching wood to steel framing. The benefit of grade-410 stainless steel is its hardness, typically approaching C-34 on the Rockwell hardness scale. Because grade-410 stainless steel does not offer the highest level of corrosion resistance, a corrosion-resistant coating often is applied to these fasteners. The coating greatly elevates the fastener's corrosion resistance and is both durable and uniform so the threads and drive recesses are not filled when the coating is applied. These screws are available in both a slender finishing head that is less conspicuous and a larger bugle head, which has greater bearing strength. Both the bugle head and finish head offer square drive recesses to minimize cam-out.

A new 500-series stainless-steel screw is now available that offers benefits that typical 410-grade stainless steel cannot match. As a rare alloy, the 500 series provides elevated corrosion resistance without the application of a secondary coating. This steel's corrosion resistance is approximately equivalent to 304-grade stainless steel while maintaining strength that exceeds that of grade-410 stainless steel-typically approaching C-53 on the Rockwell scale. Grades 304 and 316 are very difficult to harden to a level that permits penetration into light or medium gauge steel. The 500 series are available in bugle and trim head screws and come with square drive recesses for better drivability.

Plywood to Metal

Grade-410 stainless-steel screws also are used for attaching plywood to metal. The head diameter on these fasteners measures 0.45 inches (11 mm) and provides ample bearing for almost all types of applications. Modified truss head screws are available for wire lath to metal stud applications. These are most commonly used when stucco is applied to exterior walls. Using a screw with less corrosion resistance in this application can often lead to corroded screws, which can leach unsightly stains through the porous stucco.

Heavier Gauge Metal

For heavier metal, up to 5 gauge or 0.209-inch (5-mm) thickness, #12 by 2-inch (51-mm) and #12 by 2 1/2-inch (64-mm) screws are needed for attaching wood, plywood and fiber cement to these heavier metal members. These stainless-steel screws have shank slots to better enhance thread formation and remove any exhaust upon installation. They also are made with "wings" near the point to provide a clearance hole so the wood or fiber cement will not climb up the shank while being driven. After the drill point penetrates the metal framing, these wings break off so the threads of the fastener can gain positive engagement into the metal frame. Both #12 by 2-inch and 2 1/2-inch screws are available in 500 series for higher performance against corrosion when fastening to heavier steel. A recent addition to this product category is the #14 by 3 1/4-inch (83-mm) screw in grade-410 stainless steel, which is capable of penetrating metal up to 3 gauge or 1/4-inch (6-mm) thickness.

For applications that require a hex washer head drive, high-performance, self-drilling screws are recommended. These screws are made from an alloy called Marutex, which offers both a high degree of corrosion resistance and hardness to penetrate metal up to 0.148 inches (4 mm) in thickness, depending on the size of the screw. These fasteners are available in a wide range of sizes from #8 by 1/2 inch (13 mm) to #14 by 3 inch (76 mm) (500 series are available in #8 by 3/4 inch [19 mm] to #14 by 3 inch).

Fiber Cement Siding to Steel Studs

A final application that deserves mention is attaching fiber cement siding to steel studs. Fiber cement siding has appeal because of its resistance to termites and fire and its long service life; many manufacturers offer warranties up to 50 years. For this type of application, contractors should use coated 410 stainless-steel screws.

The Options

There are many benefits of using stainlesssteel fasteners; the key is matching the appropriate type with the application. Manufacturers continue to develop new products that are easier to install and offer better performance and corrosion resistance. It's worth the time to take a look at some of the tried-and-true and newer options to find one that works best for your job. It will save you time and frustration in the long run.

Bart Swan works in new product development for Simpson Strong-Tie, Pleasanton, Calif., and assists with sales training for the company's Swan Secure product line. Visit www.strongtie.com.