What Are Threaded Inserts for Wood – a Clear Introduction
Turning a bolt into wood will initially work, but the fine thread of the bolt will have too little grip on the wood and will loosen over time. When it comes to securing bolts in wood, you need threaded inserts for wood. But what exactly is this?
A threaded insert, which is also called a threaded bushing, is a type of fastener with a coarse wood thread on the outside and a fine machined thread on the inside. Because of this piece of hardware, you can use machine screws in wood.
You’d say screws can be used in wood, right? That’s correct, but if you want to be able to loosen the item you’ve secured on a regular basis, a wood screw will damage the thread in the wood. The thread will eventually disappear, and you will no longer be able to use a wood screw in that hole.
For these cases, it is better to use threaded machine screws in combination with wood insert nuts. Then, securing a bolt into wood becomes perfectly possible.
I often use wood inserts for bolts in my woodworking jigs where I use buttons to set the jig in a certain position. It allows me to do this over and over again and let me apply enough force to set the jig.
In this article, I will show you threaded inserts for wood in detail, giving you a quick insight into which projects you can use this fantastic piece of hardware.
- How Do Threaded Inserts For Wood Work?
- What Types of Threaded Inserts for Wood Are Available?
- Threaded Insert vs Tee nut, What Is the Difference?
- What Material Are Threaded Inserts For wood Made Of?
- What Are the Most Common Threaded Inserts Sizes?
- What Size Hole Do I Drill for a Threaded Insert?
How Do Threaded Inserts For Wood Work?
The wood insert nut is screwed into the wood after you have made a pre-drilled hole. As you screw in the threaded insert, the outer threaded shank engages the material. This creates a strong connection that will not rotate in the hole when a bolt is screwed into the threaded insert.
Nut inserts for wood have a flat head that allows it to be completely recessed into the wood and never gets in the way or creates a gap between the two parts connected with this type of fastener.
What Types of Threaded Inserts for Wood Are Available?
The different types depend on the manufacturer. Each manufacturer will offer a different type, allowing them to offer “unique” nut inserts for wood. The biggest differences in the types of threaded inserts for wood can be divided into two large groups: threaded inserts with fine threads and threaded inserts with coarse threads.
Fine threads are recommended for use on hardwoods. Due to the finer thread, it is easier to attach to the harder wood. Because the thread is finer, it also has more revolutions around the shaft, increasing the grip on the wood in this way.
Coarse threads are perfect for use in softwood. The thread is wider so that it will penetrate deeper into the wood and grip. This prevents the softwood from releasing the insert when subjected to greater forces.
These are suitable threaded inserts for plywood. They can be installed fairly easily in the plywood provided the correct pilot hole and are firmly anchored in the wood. You can also use these wood inserts for bolts for MDF without any problems.
If you want to know more about pilot holes, I suggest you read my article, Is A Pilot Hole Necessary? Clearly Explained For The Best Result!
You should also know that there are separate threaded inserts for plastic and metal, but since this website is about woodworking, I won’t go into more detail here.
Regular Threaded Inserts or Self Taping Threaded Inserts
Some manufacturers also offer self-tapping threaded inserts. But beware, this does not mean that you no longer have to pre-drill. With these types, you still have to pre-drill, albeit slightly smaller. Due to the self-tapping effect, the insert will then screw itself deeper into the wood than a regular wood insert nut.
Threaded Insert vs Tee nut, What Is the Difference?
The tee nut (T-nut) is an insert that will also serve to drive and hold bolts into the wood, just like the wood insert nut. However, there is a big difference in the grip and strength of the attachment and thus serves a very different purpose.
The tee nut is not screwed into the wood like the threaded insert but is driven into a pre-drilled hole. Thanks to the small pins on the inside of the tee nut, it will anchor itself in the wood.
Tee nuts are quicker to apply, but can easily be pulled out of the wood again if used incorrectly. The application is therefore completely different from the nut inserts for wood. You can find more details about the t-nuts in my article, What Are T-Nuts for Wood – a Clear & Detailed Guide.
Personally, I will be using tee nuts when using a bolt to attach parts through the back of the material. By installing the tee nut at the front of the material, and letting the screw enter through the back, the tee nut is pulled harder against the wood the more you tighten the bolt. If you insert the bolt from the front, the tee nut will be pulled out of the wood with little effort.
Check out the tee nuts I use on Amazon.
In addition to the advantage of the quick application, the tee nut does have the disadvantage that it will not be sunk into the wood and that a gap of 1 to 2 mm will be created between the two connected parts. You can always solve this problem by drilling a shallow hole with a Forstner drill bit, which is one of the 7 Essential Types Of Drill Bits For Woodworking I describe in this article.
By knowing the difference between tee nuts vs threaded inserts, you now will be able to make the right choice depending on the needs of the project you are working on. I use both of them and I think they both work well, they just have to be geared to the goal you want to achieve.
What Material Are Threaded Inserts For wood Made Of?
Threaded inserts for wood are available in a variety of metals, the most common being: brass, steel, and zinc. The type used depends on the application and the material to be cut. Every metal has advantages.
Brass inserts are easier to manufacture, which means they are cheaper. Brass is also fairly corrosion-resistant, which expands its application possibilities.
Brass inserts are most popular for use in plastics and to a lesser extent for wood.
Steel is used for inserts because it has a high tensile strength and is also generally stronger than brass. This makes it more difficult to manufacture and subsequently more expensive. However, steel is susceptible to corrosion. Fortunately, there are also threaded inserts in stainless steel, which are slightly more expensive.
Steel is the best choice for use in hardwoods.
Zinc-threaded inserts are used on soft and processed wood. They have a yellowish color. Zinc has a low melting point for a metal, making it ideal for injection molding with a fast and efficient manufacturing process. It is not as strong as brass or steel, which is why it is mainly used in wood. Zinc reacts with the oxygen and carbon dioxide in the atmosphere to form a protective layer that prevents corrosion.
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What Are the Most Common Threaded Inserts Sizes?
Nut inserts for wood are offered in many sizes. For woodworking, there are only a few sizes that are interesting, and they are:
- M4 x 10 mm (3/8”) Buy these threaded inserts on Amazon here
- M5 x 15 mm (5/8”) Buy these threaded inserts on Amazon here
- M6 x 15 mm (5/8”) Buy these threaded inserts on Amazon here
- M8 x 15 mm (5/8”) Buy these threaded inserts on Amazon here
- M10 x 15 mm (5/8”) Buy these threaded inserts on Amazon here
Larger sizes are also still available, but are often less used in woodworking. Depending on the manufacturer, longer inserts can be offered in the same diameter (M8 x15 mm (5/8”), M8 x20 mm (13/16”), …).
What Size Hole Do I Drill for a Threaded Insert?
Ok, threaded inserts need to be pre-drilled, you could read that before, but the question is, What Size Hole Do I Drill for a Threaded Insert?
Actually, there is a simple rule that you can use to know the threaded insert pilot hole size.
To drill a pilot hole for a wood insert nut, use a brad point drill bit with the same diameter as the shank of the threaded insert. Please note, DON’T use the full diameter of the insert including the screw thread, but only the body!
The depth of the drill hole must be at least 2 mm deeper than the length of the insert. So if your insert is 13 mm (1/2”), drill a hole about 15 mm (5/8”)
Measuring the body can be a bit difficult because of the screw thread, so I have this handy chart where you can easily read the threaded insert pilot hole size.
|Threaded insert size||Outside diameter||Recommended pilot hole size||Hexagon drive size|
|M4||8 mm – 5/16″||6.5 mm – 1/4″||4 mm|
|M5||10 mm – 3/8″||8 mm – 5/16″||5 mm|
|M6||12 mm – 1/2″||10 mm – 3/8″||6 mm|
|M8||16 mm – 5/8″||14 mm – 9/16″||8 mm|
|M10||18.5 mm – 3/4″||16 mm – 5/8″||10 mm|
Now you know all about threaded inserts, you are ready to use them. To know how to do it correctly, you should check out my quick and easy step-by-step guide on how to install a threaded insert in wood.
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