Threaded Rod For Custom Bolts
You can use threaded rod (often called All-Thread) for a million things. Make a long bolt, or just the right size fastener. It’s also good for special brackets if you weld to it. And, if you’re not careful, you can make it fail in a million ways too. Here are some tricks for success when cutting, bending, welding and torquing it. It’s not magic, but you should think about a few of these before finding out the hard way that threaded rod doesn’t always work the way you think.
Not All-Thread Is The Same
Sorry about the silly play on words. Just like with regular bolts, threaded rod comes in different grades (materials) for different strengths. The stuff you buy at the local hardware store is almost certainly not rated. In other words, it’s grade 2 or below, which is also the most common.
Other threaded rod grades which are stronger include ASTM A449 (Grade 5) and ASTM A354 (Grade 8). Though stronger, these are also harder to cut and form if that’s what you need. Neither of these are as common.
The other pretty common all-thread is B7. It’s ASTM A193 which is a high strength 4140 alloy steel if that means anything to you. B7 threaded rod is also good with heat.
Finally, there are several other grades of threaded rod, including various versions of Stainless Steel and aluminum, but they are less common and harder to get. If you’re interested in more detail, visit this page from Hunker.
Typical lengths are 36″, 48″ or 72″. I’ve also purchased it in 120″ lengths. Or, the Metric standard is one meter, and two. You can probably find longer, but I haven’t looked.
Easily Cutting Threaded Rod
It’s not very often that you need a bolt that is a full meter long (metric). Or the full (imperial standard) length as noted above. Anyway, that means you’ll probably need to cut it — and that can lead to a couple problems. So, before ending up with damage to the treads, think about these things.
Note, this applies with all the other factors in Choosing the Right Bolts. It also applied to cutting existing bolts to proper length.
First, use something soft to hold the all-thread. Something simple like wood in the vise to hold it will do the job.
Second, if you worry, put a nut on the rod just inside the cut so after cutting, you can twist the nut off and it will “clear” the threads. This works for quick and easy deburr, and it’s especially nice if you can’t use other deburr methods (like if it’s already fastened in an awkward location). However, read below for the better methods.
The nut on the rod can also serve as your cutting guide. The pair of nuts shown, jam together so they won’t move, do just that. Just run the hacksaw blade on the side of the nut. (Yes, it will scar the nut, so when you finish, just throw it away.)
Third, start slow. With a hack-saw, it’s pretty easy to have it “skip” over and damage some of the other threads if you’re not careful. Start slow and that’s not as likely to happen. Same is true using a handheld abrasive cutter.
Fourth, finish slow. Banging through it, or letting it bend out when finishing the cut will also damage the threads. Finish careful and smooth to minimize that.
Finally, when cutting equal length threaded rod studs, use the first as a guide to cut the rest. It’s as simple as setting them in the vise together, then running the saw on the end of the first. See the image below.
Proper deburr after cutting is the key to making the end accept a nut nicely. There are several ways to accomplish this including a file, a thread file, or my favorite. I don’t recommend finishing with an abrasive grinder as that leaves a pretty rough surface that can be as bad as the cutting burrs. Choose a file instead.
Here is a video of my favorite approach. It’s quick and easy, and works pretty flawlessly.
Bending Threaded Rod
It’s a chunk of steel, so bend it to fit the need — Right? Well, sometimes.
Failures in metal often begin with cracks at what we call “stress risers”. That’s a fancy word for areas where loading, stress, concentrates. With a bent threaded rod, that is at the thread roots in the bend. Here’s a typical bend, then below it, a close-up of the threads in the bend.
The tight bend stretches the areas between the threads. Depending on the material, this deformation can cause small cracks in the valleys between the treads. Those are frequently the failure point for threaded rod that is bent. Either way, when loads are applied over this area, the stress risers are significant. That means a threaded rod is weaker with a bend. It doesn’t mean you can’t do it, it just means you need to know it’s not as strong as normal.
The tighter the bend, the worse the condition, so the easiest way to maximize strength with a bend, is to make the bend over a bigger radius.
In this case, bending the threaded rod over something with a bigger radius. A good rule of thumb — Make the radius you are bending over at least the same as the outside diameter of the threaded rod. Bigger is better, but that depends on your needs.
The other trick you see in this image is the sleeve. In order to make the rod bend at the point we want (and not warp the rest of the rod), simply put a sleeve over the rod. This is just a chunk of round steel tube that’s a little larger than the all-thread. Working the end up as the rod bends allows the bend to start and finish in the right places.
Anytime all-thread is formed — like bent or something it’s weaker than when it started. Please take that into consideration when applying loads and torque. I’ve seen a lot of times when a chunk of threaded rod was bent, then broke when torquing the nuts. That’s obviously not the best, so take care in making the bends, and use a larger radius when possible.
Also note that the medium strength steels, like Stainless and B7 tend to work better for this. The cheap box store Grades can be a mixed bag — some will do fine, and some will crack right off.
All-Thread for U-Bolts
Sometimes U-Bolts are hard to get in the size you need. The simple solution . . . . bend one out of All-Thread. This works fairly well when the U-Bolt is a real U shape with a full round end, but not so much when the U-bolt need is actually a rectangle shape with square-ish corners.
As an option, consider making the U-Bolt not a U at all. If there’s room, leave the all-thread straight, and use a cross bar for the end of the U. This preserves the strength of everything all around, and you can make the end plates as thick as needed.
Again, this won’t work for every situation, but it can certainly help in some.
Thanks for joining us for this short discussion about threaded rod. It’s extremely useful, so make the bolts you need, and try out some of these techniques (if you haven’t already).
Also, if you know of other good tricks using All-Thread, please let us know. Our customer submission page is a great place for that.
For more reading, see our post on saving money on bolts and other fasteners.