Until the 18th century, wood was held together by nails, adhesives, or by cutting shapes to create wood joints. Each had its advantages and disadvantages, but the invention and mass production of the wood screw introduced a new method of fastening wood as well as mounting material to the wood.
Common Screw Sizes
Screws come in many different sizes, but there are three that are considered the most common.
#6 Screw Diameter
The #6 is not the smallest screw, but it is commonly used for putting together small objects. The thread size of the #6 screw is 0.13″ or 9/64th of an inch in diameter. You can find #6 screws in lengths that range from ½″ up to 1-½″.
They are most commonly used for hinges, drawer slides, light-duty fixtures and jigs, toys, and so forth.
#8 Screw Size and Its Uses
The is also one of the most common for putting together a wide range of wooden objects. The #8 screw size is 5/32 of an inch or 0.16″ in thread diameter.
It is a general-purpose screw most often found in furniture, light construction, cabinets, and more. You can find them in lengths of 5/8th of an inch up to 3″.
#10 Screw Size & Its Uses
The #10 is larger and therefore reserved for heavier jobs. The thread diameter of a #10 screw is 0.19″ or 3/16th of an inch.
You will see this type of screw used in many construction jobs. They are also used to put together heavy furniture along with outdoor or patio furniture. You can find them in lengths of ¾″ up to 4″.
You can find the other screw dimensions in the wood screw size chart further down in this article.
What is a Wood Screw?
The wood screw consists of a head that normally fits a specific type of screwdriver such as flathead, Philips, or other types. Below the head is the shank which can range from less than an inch up to several inches or more depending on its design. The shank itself is tapered which makes it easier to drive into the wood.
On the shank is the thread which secures the screw in place once it is driven into the wood. The advantage of the wood screw over the nail is its ability to be removed by reversing the driving process. Plus, the thread allows the screw to be held in the wood far more securely compared to the nail.
The original wood screws were made by hand and are easily recognized by the irregular shapes of the thread. By 1760, new manufacturing processes allowed for the mass production of wood screws that had even threads. By the mid-1800s, advanced tools were developed to make the screws far more uniform in nature.
Today, these screws are made using screw turning machines that can produce a large number in a relatively short time.
Screw Head Types
The most commonly used wood screw is the flathead screw that has a flat top and the underside of the head is tapered (conical) towards the shank. You may need to do countersinking to ensure that the screw top is flushed or slightly inside the material.
The other types of wood screws include roundhead and Panhead with a rounded top and flat bottom head. These types of screws either have their heads protruding out of the surface of the material or they site inside a counterbore.
The wood screw comes in different widths and lengths for different jobs.
Anatomy of a Wood Screw
The measurements of the wood screw consist of four different parts. The standard screw size depends on the country or region they are meant to be used. While the metric system is the most popular, for American screws, the Unified Thread Standard is used.
The thread diameter or the major diameter is denoted by using a numerical system where each number represents a specific diameter of the thread itself. For example, a thread diameter that is 9/64th or 0.13″ is referred to as #6.
The thread diameter sizes range from #0, which is 1/16th of an inch up to #14, which is 1/4th of an inch. They may be larger sizes as well depending on the chart being used.
The root diameter is the shank itself that is beneath the thread. The inner groove of the thread reaches the root diameter of the shank. You could consider this as the equivalent of a core diameter in a threaded hole.
Generally speaking, the root diameter of the screw is less important in terms of information compared to the thread diameter, because this dimension is standardized depends on the outer diameter and pitch. But for some, it may be of importance depending on the amount of material that the root of the screw will occupy.
This is the basic length of the screw itself. This means that when you purchase a half-inch screw, it will be one-half of an inch in length.
It is important to note that, the length of a flathead screw is the total length from the top of the flat to the bottom of the screw whereas in the case of Panhead and rounded head screw the length is calculated from the bottom of the head to the end of the shank.
This is the diameter or radius of the head which sits at the top of the screw. The diameter of the head will vary from different sizes of screws depending on the type of job it is performing. Some will have wide heads that allow for a flathead or Philips screwdriver to be used. While others may have a much smaller head so that it is less noticeable in the wood.
Wood Screw Size Chart
|Screw Size||Thread Diameter
Do Wood Screws Need Pilot Holes?
You can drive wood screw with or without pilot holes depending on the size of the screw, type of wood, and thickness of the material. Pilot holes help prevent splitting and cracking which can happen when screws are driven into dry or brittle woods especially close to the edges. You don’t need a pilot hole if you’re driving a #6 or #8 self-tapping screw into softwood.
Click the above link to download a printable version of the wood screw sizes with pilot bit size.