Homemade Rivnut Tool – The Ultimate DIY Guide To Setting Threaded
A homemade rivnut tool is a simple assembly of a high-strength Grade 8 bolt, a nut, and a few washers used to compress a threaded insert into a pre-drilled hole. This DIY method provides a permanent, threaded mounting point in thin sheet metal or tubing without the need for an expensive professional rivet nut gun.
Have you ever been working on a project—perhaps mounting a new rack to your truck bed or building a custom metal workbench—and realized you have no way to secure a bolt into thin-walled metal? Tapping threads into thin material is a recipe for failure, as there simply isn’t enough “meat” for the threads to grab. This is exactly where a threaded insert, often called a rivnut, saves the day by providing a robust, permanent nut inside the material.
While professional rivet nut guns are great, they can be a significant investment for a one-time repair or a small weekend project. You might find yourself staring at a pack of inserts but lacking the $50 to $100 tool required to install them properly. The good news is that you can build a highly effective homemade rivnut tool using a few dollars’ worth of hardware from your local shop.
In this guide, I will walk you through the physics of how these inserts work and show you how to assemble your own setter. We will cover the specific hardware grades you need to avoid stripping threads and the step-by-step technique to ensure a tight, professional fit every single time. By the end of this article, you will be able to tackle metal fabrication projects with the confidence of a seasoned pro.
Understanding the Mechanics of Threaded Inserts
Before we build the tool, we need to understand what we are trying to achieve. A rivnut (or rivet nut) is essentially a hollow, threaded sleeve with a collapsible body. When you pull the threaded portion toward the flange, the unthreaded middle section bulges outward, gripping the backside of your workpiece.
This “bulging” action requires a significant amount of linear force. A professional tool uses a lever or pneumatic piston to pull the internal mandrel. Our homemade rivnut tool achieves this same result through the mechanical advantage of a screw thread. By holding a nut stationary and turning a bolt, we convert rotational force into the heavy-duty pulling force needed to crush the insert.
It is important to note that the material thickness matters. Every insert has a “grip range,” which is the thickness of the metal it can effectively clamp onto. If your metal is too thick, the insert won’t collapse; if it is too thin, the insert might spin freely in the hole. Always check your insert’s specifications before you begin drilling.
How to Build Your Own homemade rivnut tool
To build a reliable setter, you cannot just grab any old bolt from your junk drawer. You need components that can handle high torque without snapping or deforming. Standard hardware store bolts (Grade 2 or 5) are often too soft and will likely strip their threads before the rivnut fully collapses.
Here is the list of materials you will need for a standard M6 or 1/4-20 insert:
- One Grade 8 (or Class 12.9) hex head bolt, at least 2 inches long.
- One matching Grade 8 nut.
- Two hardened flat washers.
- One “oversized” nut (one size larger than your bolt) to act as a spacer.
- High-pressure grease or anti-seize lubricant.
The assembly is straightforward. Thread the nut onto the bolt several inches, then slide on the two washers followed by the oversized “spacer” nut. The oversized nut is crucial because it allows the rivnut’s flange to sit flat against the workpiece while the bolt pulls the internal threads upward through the center. Applying a small dab of grease between the washers will significantly reduce friction, making the installation much smoother.
Choosing the Right Hardware: Grade 8 vs. Standard Bolts
The most common mistake beginners make is using “zinc-plated” Grade 2 bolts. These are fine for hanging a picture frame, but they are far too weak for a homemade rivnut tool. When you apply the necessary torque to crush a steel or stainless steel insert, a soft bolt will stretch and eventually fail, potentially ruining the insert and your workpiece. Grade 8 bolts, usually identified by six radial lines on the head, are made of medium carbon alloy steel and are quenched and tempered. They offer a much higher tensile strength. For metric sizes, look for “Class 10.9” or “Class 12.9” markings. These hardened fasteners can withstand the repeated stress of setting multiple inserts without the threads galling or flattening.
In addition to the bolt grade, consider the material of the insert itself. Aluminum inserts are the easiest to set and are perfect for light-duty applications. However, if you are working on a vehicle chassis or a heavy equipment repair, you should use steel or stainless steel inserts. These require significantly more force to set, making the use of high-grade hardware in your DIY tool even more critical.
Step-by-Step: Setting Your First Insert
Once your tool is assembled, it is time to put it to work. The process requires a bit of “feel,” so I always recommend practicing on a scrap piece of metal that is the same thickness as your actual project. This allows you to gauge how much force is required before you commit to the final piece.
- Drill the hole: Use a high-quality drill bit to create a hole that matches the outer diameter of the insert. It should be a “snug” fit—if the hole is too large, the insert will spin.
- Deburr the edges: Use a deburring tool or a larger drill bit to remove any metal burrs from the hole. A clean surface ensures the flange sits perfectly flush.
- Thread the tool: Thread your DIY assembly into the rivnut until the bolt is fully engaged with all the internal threads of the insert.
- Position the tool: Insert the assembly into the hole. Ensure the flange of the rivnut is pressed firmly against the metal surface.
- The Two-Wrench Technique: Use a box-end wrench to hold the “setter nut” stationary. Use a second wrench (or a socket) to turn the bolt head.
- Compress: As you turn the bolt, you will feel increasing resistance. This is the insert collapsing. Continue until you feel a distinct “bottoming out” sensation.
- Reverse and Remove: Hold the nut stationary and back the bolt out. Your threaded insert is now permanently installed.
The Importance of Hole Precision and Deburring
In metalworking, the quality of your finished product is often determined by the preparation phase. When using a homemade rivnut tool, the hole diameter is your most critical variable. If you use a bit that is even 0.5mm too large, the knurled body of the insert won’t have enough friction to stay still during the initial compression.
If the insert begins to spin while you are trying to tighten the bolt, the installation becomes much more difficult. To prevent this, always use a sharp step-bit or a dedicated metal-cutting twist bit. If you find the insert is spinning, you can sometimes stop it by applying more downward pressure on the tool or by using a small amount of serrated washer between the tool and the insert.
Deburring is not just about aesthetics; it is about mechanical integrity. A burr trapped under the flange can prevent the insert from sitting square. Over time, vibration can cause that burr to flatten, leading to a loose insert. Take thirty seconds to clean the hole with a countersink bit for a much more professional result.
Troubleshooting Common DIY Rivnut Issues
Even with a well-made homemade rivnut tool, you might encounter a few hiccups. The most frequent problem is “spinning.” This happens when the insert rotates in the hole instead of collapsing. If this occurs, try using a pair of pliers to gently hold the flange, or use a star-type lock washer between your tool’s spacer nut and the insert to provide extra grip.
Another common issue is over-tightening. It is tempting to give the bolt one last “ugh” of torque, but this can strip the internal threads of the insert or the bolt itself. You are looking for a firm stop, not a test of your physical strength. Once the resistance increases sharply, the insert is likely fully collapsed against the backside of the metal.
If you find that your bolts are snapping frequently, check your lubrication. Metal-on-metal friction creates heat, which leads to galling—a process where the threads effectively weld themselves together. A drop of motor oil or a smear of lithium grease on the bolt threads and between the washers will prevent this and extend the life of your DIY tool.
When to Upgrade to a Professional Tool
The DIY approach is fantastic for small projects, but it has its limits. If you are a garage DIYer planning to install fifty inserts in a single afternoon, your hands and wrists will likely tire of the manual wrenching. The homemade method is significantly slower than a dedicated lever-action tool.
Professional tools also offer stroke adjustment. This allows you to set a specific “pull distance,” ensuring every insert is collapsed exactly the same amount. This consistency is vital for structural applications where torque specs are strict. If you find yourself using threaded inserts on every project, a professional long-handle setter is a worthy investment for your workshop.
However, for the occasional repair or custom bracket, the homemade rivnut tool remains the king of cost-effectiveness. It takes up almost no space in a toolbox and can be built for multiple sizes (M5, M6, M8) for a fraction of the cost of a multi-head kit. It is a classic example of using basic mechanical principles to solve a complex fastening problem.
Safety Practices for Metalworking and Tool Use
Safety should always be your primary concern when working with high-torque tools and metal. When using your homemade rivnut tool, always wear impact-rated safety glasses. If a Grade 8 bolt were to snap under extreme tension, the fragments could fly off with significant force. Protecting your eyes is a non-negotiable step in any shop.
Be mindful of your hand positioning as well. When using the two-wrench technique, it is easy for a wrench to slip if it isn’t seated properly on the nut or bolt head. This can lead to “knuckle busting” against sharp metal edges. Whenever possible, pull the wrench toward you rather than pushing it away, which gives you more control if the tool slips.
Finally, always inspect your hardware after every few uses. Look for signs of thread stretching or “thinning” on the bolt. If the bolt looks slightly elongated or the threads appear shiny and flattened, discard it and use a fresh Grade 8 bolt. Fasteners are cheap; your project and your safety are not.
Frequently Asked Questions About Homemade Rivnut Tools
Can I use a standard zinc-plated bolt for this?
It is not recommended. Standard Grade 2 or Grade 5 bolts are too soft. The high torque required to collapse a steel rivnut will likely strip the threads of a soft bolt, potentially getting the tool stuck inside the insert.
What do I do if the rivnut starts spinning in the hole?
Try to increase the friction between the insert flange and the tool. You can use a serrated lock washer or a piece of sandpaper between the tool’s spacer and the insert. Ensure the hole isn’t drilled too large for the insert size.
Can I install stainless steel inserts with a homemade tool?
Yes, but it requires significantly more physical effort. Stainless steel is much harder than aluminum or mild steel. Ensure you are using a high-quality Class 12.9 bolt and plenty of lubrication on the threads to prevent galling.
Do I need to use a spacer nut?
Yes. The spacer nut (which should be larger than the bolt diameter) allows the bolt to pull the bottom of the insert up without putting pressure on the flange itself. It also provides a stable surface for your wrench to hold the assembly steady.
Final Thoughts on Mastering the DIY Rivnut Method
Building and using a homemade rivnut tool is a rite of passage for many DIY enthusiasts. It teaches you the value of mechanical advantage and the importance of material science in the workshop. While it may take a few extra minutes compared to a professional tool, the results are just as strong and reliable when done with care.
Remember to prioritize high-quality fasteners and precise hole preparation. These two factors alone will determine whether your project is a success or a frustration. Whether you are working on a custom vehicle build, home furniture, or shop organization, having the ability to create permanent threads in thin metal is a massive upgrade to your DIY skill set.
Go ahead and gather your hardware, grab your wrenches, and give it a try on some scrap metal. Once you see how easy it is to achieve professional-grade fastening with just a few bolts and nuts, you’ll find yourself looking for reasons to use threaded inserts in every project. Stay safe, work smart, and keep building!
