A screw isn’t anything special, right?
That couldn’t be further from the truth.
These everyday items vary drastically in several ways.
The research, design, and manufacturing process behind woodworking screws is truly fascinating.
It’s easy to overlook the details of something so tiny which people tend to take for granted.
You probably already know that wood screw sizes vary but beyond that, how do you know you’re selecting the right wood screws for the job?
Using the wrong type for your project can be downright dangerous depending on what you’re building – these items are not created equal.
The Design and Fabrication Behind Woodworking Screws
Like many construction devices, the first use of a threaded material for joining items together likely originated in ancient Egypt and was made of wood.
The metal threaded device as we (somewhat) know it was patented and tweaked in 1760. The thread design and details have changed drastically over the past few centuries with the advent of commercialized metal in the western world.
1. Material
These fascinating items can be made from a variety of metals and alloys such as
- Low and medium carbon steel
- Stainless steel
- Brass
- Nickle
- Aluminum
Finishes are often applied to screws which have a direct impact on the item’s strength, brittleness, and toughness (yes, these are three distinct technical qualities).
Coating substances often include
- Zinc
- Chromium
- Nickle
- Cadmium
Low or medium carbon steel is ideal for woodworking screws due to its strength.
2. Manufacturing Process
The steel for these common items starts out as wire on a spool.
Through a cold manufacturing process, the steel wire feeds into a pre-programmed machine which cuts the head into a precise shape using a die.
From there, the blanks are fed into what’s called a vibrating hopper which guides the items into the thread rolling machine.
After they’re finished, they travel through a heat-treating process.
This entire manufacturing process varies depending on the type of screw and – again – impacts the item’s strength, ductility, and toughness.
3. Recess Design
In general, woodworking screws are available with three different recessed designs which affect the amount of torque during application.
- Slot head
- Phillips recess
- Square drive
The slot head recess isn’t ideal for many heavy-duty projects because it’s easy for the drill to slip during application.
The Phillips recess is one of the most popular throughout woodworking thanks to its grip potential when driving the screw into the wood. The downside? The Phillips recess often results in damaging the shape due to high torque. This is also known as “cam-out.”
The square drive is very popular throughout woodworking because it reduces cam-out and requires less pressure during application.
4. Head Design
There are lots and lots of different head designs. Each has its own characteristics, advantages, and disadvantages.
Most of the common head designs found throughout wood screws include
- Flat head: the top is flush with the wood surface
- Oval head: a slight oval surface with countersink design
- Trim head: the top is flush with the wood surface, but the diameter is smaller
- Truss head: a dome shape with a large bearing surface and low-profile head
- Pan head: a dome shape that sits on top of the wood surface
- Washer head: a very large bearing surface
Always make sure you select the best head design for your specific project – they have a direct impact on your woodwork’s strength and durability.
5. Thread Design
On “new” wood screws, the threads stick out farther than the shaft. This very slight alteration has a big effect on the screw’s ability to “grab” the wood itself.
Thread design is a big area where dry wall and wood screws differ. In drywall varieties, the countersink is slightly concave while in wood varieties it has an almost 90° angle.
“Double lead” threads are also common in wood varieties which includes a set of parallel threads.
As particle board and cheaper wood becomes more common, this modest fixture has evolved to compensate for new low-quality materials. (With help from manufacturers and engineers, of course.)
6. Wood Screw Sizes
When it comes to wood screw sizes, you have over 20 distinct options to choose from – all of which are measured by thread diameter.
#0 is the widest at 0.060 inches and the sizes go down as the number goes up.
Which number should you use? That depends on the type of wood you’re working with and how much strength is required.
How Do You Select the Best Screw for the Job?
There’s no definitive answer for this – it depends completely upon the type of wood and project.
One thing is certain: you should absolutely never use drywall varieties for wood.
Drywall screws are much more brittle and can be dangerous when used with wood.
