Types Of Screws And Fasteners For Structural Woodworking

Woodworkers have always used different screws and fasteners for structural work than other assemblies that require less holding power. There is quite a bit of variance between the screws and fasteners carried by suppliers like Marafast.com for interior applications and exterior work as well. In some cases, the fasteners for both interior and exterior work were the same design, but the exterior version was coated in order to avoid corrosion. Because of the need to have fasteners for interior locations where corrosion was a problem, exterior fasteners were sometimes specified for work in bathrooms, kitchens, and basements.

Hot-Dip Galvanizing for Exterior Work

For many years, the most common type of screws and fasteners for exterior structural woodworking were lag screws. Lag screws were the preferred fasteners when absolute strength was required when joining timbers. Lag screws were one of many types of exterior screws and fasteners that were hot-dipped in zinc to galvanize them against rust. Hot dipping is superior than electroplating for fasteners that will see heavy exposure to the weather. For exterior applications, things like joist hanger and similar metal brackets aren’t suitable because the electroplating is too thin to stand up to freeze-thaw cycles and lots of rain and snow. They’re only acceptable for use in moderately damp locations like basements. That’s why you see screws and fasteners that are hot-dipped in zinc in outdoor locations.

Lag Screws Require Careful Pre-Drilling

Hot-dipped lag screws are very labor-intensive to use. They require quite a lot of pre-drilling in order to work properly. This pre-drilling also must be done to fairly tight tolerances to achieve the maximum strength in the resulting join. For instance, if the pre-drilled hole for a lag screw is too large in diameter, the threads on the shaft won’t grip effectively, and the screw can lose its hold under strain. If the hole is drilled too small, it might be impossible to drive the screw all the way in, and attempts to force it can result in shearing off the head of the bolt, or splitting the timbers being joined.

New Screws Let You Skip Pre-Drilling

New types of screws and fasteners are being introduced all the time. The latest types of structural screws are made from rust-resistant metals, which make it unnecessary to dip them in zinc for rust proofing. They’re thinner than lag screws, enabling the installer to drive them using less powerful tools, including cordless drill drivers. The tip of these new screw types is razor sharp, and starts easily, even in wet timbers. The shank of the screw is thinner, so it doesn’t require pre-drilling the way lag screws do.

At the end of the screw threads, there’s a series of flutes that enlarge the hole to accept the final smooth shank with less force required to set the head flush. To save money and trouble, these screws can have a built-in washer head that spreads the force applied to the screw over a larger area, and avoids crushing wood fibers. These screws also use insert heads instead of hex heads, and with torx patterns, they avoid cam-out problems and stripping, even under heavy torque.