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Choosing the optimal wood screw — size, strength, and silhouette
When choosing the ideal wood screw, remember that fasteners are not intended for universal application. Nor are all screws created equal. Manufacturers like SFS engineer a broad array of fasteners to address specific use cases and needs. Therefore, don’t focus on finding the overall best wood screw, but rather the one that best fits your particular project’s specs.
Make sure to use the right type of screw
Using wood screws interchangeably may get the job done, but you also jeopardize short-term efficiency and long-term results. Common types of wood screws include:● Wood to wood structural screws — Common uses for structural screws include framing, deck construction, and structural interior panels. Self-drilling versions of the screw need to pierce two separate layers without splitting the wood, requiring a specially designed point. To further familiarize yourself more with wood-to-wood screws, explore our ConnexTite™ collection.
● Metal to wood screws — These screws (often used for exterior paneling) tend to be shorter than structural screws. For examples of screws designed specifically for metal-to-wood connections, check out our Woodgrip™ product line and our selection of long-life fasteners.
Recommendations for finding the right sized wood screw: length, gauge & dimensions
The thickness of the attached materials should be top of mind when assessing wood screw options. We recommend that the fastener’s shank be the length of the top attachment plus ⅔ of the bottom layer depth. However, if this is not achievable due to the ample thickness of the receiving wood, aim to have the screw length be, at minimum, the full length of the attachment plus ½ of the bottom’s depth.A wood screw's sizing also encompasses the gauge (the exterior thread diameter). Think of #8 as your baseline; thicker and/or heavier attachments require greater gauge measurements while fine pieces benefit from a reduced hole size.
Keep in mind, these are general sizing recommendations. For a deeper explanation, please refer to our article 'How to choose the correct screw length' or contact a member of the SFS team for project-specific guidance.
Factor in the multiple types of wood screw strength
In regards to wood screws, “strength” is a fairly broad term that can mean one (or more) of the following:● Shear strength — the amount of weight a fastener can support perpendicular to its body before compromising its structural integrity. This is particularly important for screws laterally applied since the connected wood or panel places increased force on the shank.
● Tensile strength — The amount of parallel strain a screw can endure before breaking.
● Torque strength — The maximum rotational force which can be applied to the fastener.
● Pull out strength — This common phrasing refers to the fixation strength of a screw, meaning the amount of force necessary to pull out a screw when optimally fastened.
All of this information can be found on individual screws’ datasheets. In the example below, #9-15 Woodgrip™ Metal to Wood Fastener specifications detail its various strengths in addition to the screw sizing options, intended application, and product features. As you’ll notice from the tables, the deepness of the screw correlates with the generated strength.
Other factors that can lead to increased (or decreased) strength include:
Whether the wood screw is fully threaded or partially threaded.
- Choice of metal and manufacturing practices. Even amongst different steels there exist nuances in the composition and treatments. For example, carbon steel is extremely strong but notably vulnerable to rust. Comparatively, stainless steel is much more resistant to corrosion (and can be costly as a result). As noted in 304 vs 316 stainless steel screws, even stainless steels have variations based on their grades. The goal is to find a wood screw that meets the mandatory corrosion resistance and strength requirements without overspending.
The necessary thread coarseness to minimize the risk of stripping
Arguably the most important indicator of pull-out strength is the coarseness of the threads. As noted in our guide Fine thread vs. coarse thread, a “coarse” design has greater distances between each thread to enable a stronger grip.Generally, wood screws are coarser than other fasteners designed for different purposes. Hardwoods are compatible with relatively finer screws, while softwoods call for larger distances between threads. In fact, certain engineered woods(link to article) like plywood or OSB are best served by specialized screws with extra-aggressive threading, such as the #12 Woodgrip™ XG, designed to minimize stripping.
High-end manufacturers like SFS thoroughly test their wood screws to determine (and improve) their varying strengths. The resulting information should be easily available within the datasheets or brochures.
Don’t forget about your wood screws’ head style
Your choice of wood screw head not only impacts the visual but also what tools contractors can use during the installation.While there are dozens of particular silhouettes, they mainly fall into two broad categories: countersunk and non-countersunk. The former sinks into the wood so its top is level with the applied surface, minimizing obtrusions from the surface. The latter bulges out, but provides stability during drilling and places less stress on the wood than their countersunk equivalents. For this reason, many contractors elect for non-countersunk wood screws unless the project requires flush application (such as with flooring)
Determine the preferred screw point type
A big determinant in choosing the best type of drill point is whether or not you want them to be self-tapping, meaning that they do not require a pilot hole prior to application. When utilized on larger projects, the time savings significantly accumulate. However, self-tapping wood screws are not without potential downsides. Mainly, if you ultimately remove the screws, you risk stripping.When browsing for the right wood screw (or talking with a consultant) be mindful of whether there are specialized points that fulfill your needs. For example, ribbed points lessen the risk of splitting wood.
