The right one for the job:
Drill through the differences among stainless-steel fasteners
Bart Swan,
Posted
05/01/2009
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.