“Screws fall out all the time. The world is an imperfect place.”The Breakfast Club (1985)
Should you use a nail or should you use a screw? It’s a question as old as time itself. Or, at least as old as woodworking. Or, at least as old as nails and screws. In order to answer this elusive question, we need to understand each ones’ strengths.
Grip Strength Vs. Shear Strength
Screws apply what is called grip strength to the two pieces you are screwing together. Grip strength is how well the fastener can draw the wood together. The threaded design of a screw causes compression between your two pieces, meaning they pull into each other at the screw point. Grip strength excels at holding together two pieces that experience forces parallel to the fastener, such as flooring or decking. Generally speaking, most projects where gravity is a weight factor will call for screws.
Nails, on the other hand, apply what is called shear strength. Shear strength is a fastener’s ability to prevent two pieces from shifting if force is applied perpendicular to the fastener. This is widely used in framing, for example. Nails excel at shear strength because they are generally more malleable than screws. They can bend (albeit slightly) to accommodate new forces. Screws can easily snap under shear pressure, as they have very little elasticity by design.
Use Your Head
There are plenty of other factors to consider before choosing. If it’s not a critical joint, you may want to use nails instead of screws because nails are easier to hide. If you’re planning or experimenting, a screw may be preferred in place of a nail simply because they are easier to remove. These are the general guidelines, but nothing is set in stone (or wood). If you know the practical applications of both and you are familiar with your project, then you know what will work and what won’t! Don’t doubt your own instincts.