How should I connect things as I build my trailer? Welding is a typical practice for many structural frame members, but bolting also has some great benefits. So, this makes me wonder. How do I decide where to bolt, and where to weld? Since it is usually not an all or nothing proposition, we will examine some differences and compare bolting or welding for trailer frames, and other trailer components.
First things first. This article is for perspective and to help with decisions. We will talk about advantages and disadvantages of bolting or welding, but we cannot possibly cover everything. There are times when bolting is a better choice, and times when welding has a clear advantage.
So, we will discuss some best practices knowing full well they do not work in every situation. Finally, we will refer to other articles for topics we have already covered.
In the end, the decision for bolting or welding for your trailer is up to you. There are some things that beg for welding, and other areas that are better with bolts. That probably means some of both in a proper build. Here we go . . . Where? and When? to bolt or weld.
Bolting, Welding and More
Starting with a pile of raw material, we turn it into something useful. When the raw material is metal, we call it fabrication – particularly when the process includes bending, shaping, cutting, drilling, welding or otherwise changing the material. Connecting those reformed pieces is the heart of this discussion.
We will focus on two methods – welding or bolting – but there are a bunch of others to keep in mind. Rivets, adhesives, nails, snaps, press-fits, snap rings, hitch pins, over-molding, tape, Velcro, straps, clamps, and crimps are examples. While we are not ignoring these, we will not discuss them in this article.
Welding is exciting with a ton of sparks flying. Welding requires planning and maybe some extra tricks like pre-stressed fabrication to make it all turn out. Bolting, on the other hand, means a bunch of holes. (I love watching a drill cut into metal with nice spiral chips.) Bolting and welding are the 2 fastening means we will discuss.
In general, there are 3 groups these fastening techniques fall into: Permanent (welding, glue), Semi-Permanent (tape, press-fits), and Removable (bolting, spring clips). Many of the properties of the discussion below will fit other processes in each category as well. Feel free to extrapolate for your project.
Philosophy For Bolting Versus Welding
From a philosophical standpoint, it is good to categorize the guiding principles. Here are 3 to guide choices in connection techniques.
- “Permanent” versus the “Removable” connections. (“Semi-Permanent” fits in there somewhere too.) If something should be a permanent connection, then make it permanent. If it there is a need to move or remove something, then make it removable. That might seem obvious, but we will look at it a little deeper below.
- Safety. If something is safety related, then the processes for connection must reflect it. For instance: extra bracing, added bolts, fasteners that will not vibrate loose, extra surface area for welding, more strength in the chosen materials, etc.. Making things with redundancy, or extra strength is a step to building for safety.
- Degradation. Vibration, rust, tampering, impact, fatigue, and wear are all aspects of degradation that happen over time. If the objects to connect will experience any of these, then we must give extra care when making the connection.
Applying The Guides
Taking these guiding principles to a trailer frame (the point of this article), here are some considerations.

- Most connections on a trailer frame are best when permanent. There are, however, notable exceptions. Some examples: Decking material may damage or rot, lights can break, tires wear out, axles require maintenance, etc.. These are best as “removable” connections.Other areas can have needs both ways – depending on context. For instance: Most trailer tongues are “permanent”, yet a folding tongue requires a “removable” connection. The same with trailer frames, but exceptions include tilt deck trailers.
- Almost everything on a trailer relates to safety because we do not want bits falling on the highway. If something comes loose, there is a significant risk of lost goods, or of hurting someone. So, we want all connections to rate high for safety – both “Permanent” and “Removable” connections.
- Trailers have all sorts of vibration, weather, impact, fatigue and wear. That means all the connections must be strong with respect to degradation over time. That means cleaning the metal before welding, then painting it after. It means using Anti-Seize on bolts, AND locking hardware.
- Many, if not most, things we add to a trailer are good with “removable” connections. This article is about trailer frames, yet since we attach things to the frame, it is worth a mention. Flexibility for making changes, or for changing options make “removable” connections important for the extras. And, they must, at some point, attach to the frame.
Note that all of these guiding principles lead to always making secure joints, but not specifically to welding or bolting (except the candidates for removable connections). That means our next step is to think about each joint in more detail.
Choosing An Attachment Process
In context of welding versus bolting for trailer frames, our next step is to look at each connection in a more detail. We need to think about advantages and disadvantages for the construction process as well as the end performance.
As we look at each characteristic, it is easy to start going down the mental path of our bias for a connection process. In many cases, welding will manage these principles better, but that is not absolute. So consider these items with respect to the desired function and outcome.
Welding vs. Bolting, What are the big differences?
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Strength.
From a strength standpoint, it is much easier to engage from one piece to another with welding. The welds can cover a lot of surface area, and they are easily set at the extremes of the contact. For instance, welding the perimeter of something is a very strong connection. Bolts, on the other hand, focus the strength in areas surrounding the bolt. That usually means you need several bolts.
Other ways to help bolting be successful – strength of fasteners, UNC vs. UNF, Locknuts (Nylock, crush, lock washers). See the Bolts 101 article.
Strength per weight, and strength per size is much easier to achieve with welding. That said, strength is not exclusive to welding.
It is important to point out that we can easily choose weak ways for connecting either way. Insufficient weld penetration, or poor choices for coverage will make welds weak. Likewise for bolts, too large or too small, or an insufficient number will make a bolt connection weak.
We can also choose ways of connecting both that strengthen the trailer frame. Proper technique is key, no matter which connection method we choose.
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Weakening Effects.
At Mechanical Elements, we teach a lot about the “Keep Out” areas for welding. Our plans point to areas of high stress and say “DO NOT WELD HERE.” We could likewise say something similar for bolting. “DO NOT DRILL HERE.” While both processes have limitations in high stress areas (welds changing the continuity of the material, and bolts removing important material), they are similar because they both create stress risers. Not a good thing.
The failure method for the two is different, however. For a weld in a high stress area, fatigue will eventually allow a crack to follow near the periphery of the weld. For bolt holes, the higher stress around the bolts can make the material stretch, or begin cracks starting in the holes. Weld fatigue typically follows the edge of the weld. Failures happening near bolt holes can go any direction. (Usually it goes the shortest distance to the next open edge.)
Anyway, with welding it is a localized material discontinuity (heat affected area) that creates an opportunity for failure. With holes, it is a reduction in material available and the constriction which creates a stress concentration. While we must know these weakening effects, proper design with proper implementation will make both fastening methods fine for a trailer frame.
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Safety.
We have covered this above. With bolting or welding, assuming proper technique and implementation, both methods are safe. The correct processes are different for bolting and welding, but both can be safe if the design is right.
One advantage for Welding. It is easier to achieve vibration resistant connections with a good weld. Assuming the materials are proper for the job, it is not over-stressed, or flexing, welds do very well with vibration.
However, when the joint design is not right, (if the weld flexes, or the material is too thin, poor weld properties, etc.) the failures are catastrophic. This image shows fatigue cracking and failure where the material near the weld will fail.
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Overlap.
For bolts to work, materials must overlap so the bolts have a place to reside. On the other hand, welds really only require the materials to contact. Without judging for strength (we did that in the previous point), a weld can join pieces at the ends. To make a bolt connection we must add overlap – either add an overlapping plate, or make the two pieces extend to overlap. Most times this means extra material for bolting.
Along those lines, for a good connection in a vibration environment (which is every trailer), the overlap must be fairly long. Often bolt connections to “work loose” so they are no longer rigid and tight. That makes, of course, for a squeaky and wobbly trailer. While this does not often lead to safety concerns (assuming the right size and use of the fasteners), it can make things a little uneasy.
The amount of overlap and number of bolts is always a good question. If the joint is in bending (has a moment), then create more overlap. If the joint is really important, increase both overlap and the number of bolts. If possible, I recommend at least 4 bolts in every overlap (spread as much as practical) for best results. Almost never is a single bolt a good idea.
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Various Materials.
When the materials are different, bolting or a similar process works better than welding. Have you ever tried to weld aluminum to steel? It does not work. Same for welding wood. On the other hand, bolting works super well for connecting materials that are different. (Though I will suggest preventive measures to avoid dissimilar metals corrosion).
We can take this one step further in the “Skill” department. There is a certain knowledge with respect to choosing welding rod (stick and TIG welder) or wire (MIG welder) along with the shielding gas. That is dictated by the materials you are welding. A good example is welding mild steel versus welding various stainless steels.
Finally, some alloys do not weld well, or do not weld well to others. They are perhaps not technically dissimilar, but high carbon steels, for instance, are usually better with bolts.
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Material Profiles
The shape of the materials to use is also a big factor in choosing the best process, bolting or welding, for a trailer frame. Round tube, for instance, is not so easy for construction with bolting without extra brackets or adapters. Bolting in the flanges of C-Channel or Standard I-Beam shapes also offers some difficulties without adaptations like wedge washers. (See the image below.)
One shape that might not be so obvious is rectangular or square tube. While it might seem easy at first (because of the flat surfaces), bolting for structural purposes is more difficult. Bolt tightening has limits without crushing the tube, at least in part. To make it work, bolts must go though just one side of the tube (like in the photo), or have spacers (or spread plates) to keep the tube from squishing.
It is actually pretty hard to get a good solid structural bolt connection through a hollow profile without some sort of adaptation.
For these reasons, welding tends is more adaptable for joining various material profiles. That is not to say accommodations are never required for welding, but when they are, it is often less involved.
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Build Flexibility.
If you want something on the trailer sometimes, but not at other times (sides, for instance), use bolts or some other form of removable connection. If you think down the road you might want to add a toolbox, or some other widget, make the bolt holes now, so adding it later is easy.
If you are notorious for backing the trailer into things, bolt-on a suspended, sacrificial bumper so it can easily remove and replace.
Another point is the build after the build. Call it add-ons. After my last trailer was complete with full powdercoat, I decided to add some extras. For me, the obvious answer was bolting because it did not require removal of the finish to weld a bracket. Just drill some holes, and the brackets bolt on.
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Construction Time.
There is some give and take on this one for bolting or welding. In general, if construction is all welding, the time to weld is often much less than measuring for drilling matching holes, then setting up for bolting. True, there is prep work before and after welding, but that usually does not compare to the prep of drilling holes. Grinding or sanding areas for welding is usually faster than, measuring, drilling, getting the right bolts, nuts, washers, and wrenches to make a good bolt connection.
Funny thing about time . . . it is more important to save time in the moment, than later when you wish you had taken a little more time to do something better, or different. How many times have I wished I had thought through the process a little deeper before making something? Live and learn. Oh well.
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Skill.
I can argue both ways on this one. Yes, there is skill in making a good weld. There is also skill in measuring well and drilling multiple sets of matching holes. The skill with the holes is getting them all to line up right, and getting them straight, every time.
There is skill in choosing both the right size fasteners, as well as, the right number, the right thickness of materials, and the right spacing for the needed strength. Even, like this photo, knowing how to compensate for materials like C-Channel.
In terms of setup and prep, welding takes similar skill in alignment, avoiding thermal pull, proper penetration, etc.. Either way, to build a good trailer, familiarity and skill with both bolting and welding are part of it.
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Equipment.
The tools are definitely different. Welding machines come in several varieties, and they all require their own set of skills. Drills for making holes (and the tools for fabricating proper brackets) are necessary for bolting. Is one group of tools more expensive or more difficult to use? I think that may depend on your perspective. See the next point. Does one method require more tools than the other? I do not have a convincing answer to that.
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Longevity.
Both Bolting and Welding have a very long expected life. We can certainly do things to reduce that life, however.
When properly cared for both options will last a long time – even in the weather. That means paint and protection from the elements mostly. With welds, it also means sealing areas that contact, like at the seams, any place there is not a bead.
With bolting, it means using anti-seize (or something similar on the threads), as well as proper paint or protection for the metal around (like in the holes). It also means choosing the right bolts with appropriate materials and finishes. Sometimes, even stainless steel bolts.
It is hard to make a call as to which is better in the long term. Even when neglected, both bolting and welding will last a long time. They may look ugly full of rust, but they last a long time.
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Have we covered it all?
Please leave a comment if we have missed something important.
Welding AND Bolting
The two methods, welding or bolting, are so related, yet very different. BUT, one key point – we usually build a trailer with both. So, all the discussion above about tools and cost of equipment, skill, etc., become somewhat moot because we need both. A purely welded trailer will not have turning wheels or any kind of suspension. A purely bolted trailer will take a bunch of extra work (and the right material choices) to avoid welding at all. Truly, a “bolting only” trailer would have a lot of limitations.
Here is a summary of the points above.
When do bolts work best? For Differing Materials, for Flexibility in construction, and for Removable Connections.
When is welding best? When Permanence is required, and when material overlap is not available, not desired, or impractical. Other things like strength are more easily achieved by welding in a smaller, more efficient way. However, strength is not exclusive of bolting.
So, for a trailer frame, welding offers a pretty quick and robust, permanent joint. Bolting offers flexibility, but usually requires more parts and space – and often requires welding anyway to attach flanges, bolt plates, etc. When choosing bolting or welding, it really depends on the design needs and the effort to get it there. I recommend choosing the method depending on the joint requirements, rather than thinking about the whole concept.
In my experience, the combination of both bolting and welding gives the best result. There may be a bias toward bolting or welding, but using both will give the better result.
Cost Comparisons
When we think about welding, sometimes we think about the cost of the welder and all the related equipment. In many ways Welding “feels” more expensive. However, I think that is a misnomer. When fabricating a trailer made for bolting, a lot of time goes into drilling holes. Not just one hole per bolt, but a hole in the frame as well as a hole in the member to bolt up. And, they must match position. That means time in measuring, marking as well as drilling. Of course, techniques like hole matching can help, but still, it takes time.
Then there is the cost of bolts and nuts and washers – which are more than welding wire and gas, for sure. However, if you do not have a welder, then it might be a moot point. That said, in general, welding is quite a bit less expensive than bolting even when using our tips about How to Save Money on Bolts.
So to say one method is more or less expensive does not do the concepts justice. I think you can do both welding and bolting cheap, or expensive – with simple or complicated tools.
Our Comparison Summary
I will guess that most of the information above is much you knew anyway. I personally think welding is the way to go for most trailer member connections, but there are plenty of situations where bolts shine. That said, I think every bolted trailer should have welding to support the bolting brackets (in the right places). The compact strength offered by welding is hard to beat with bolts.
And, I will emphasize the use of both. While I support welding for most of the structural frame, I have never designed a trailer that does not have bolts. They are both excellent attachment methods – and appropriate in their spheres. Good luck with your trailer build – Bolting or Welding!
** Just for grins, when writing this article I did a fun experiment with ChatGPT. With all the hype, I decided to give it a comparison. If you want to know what Artificial Intelligence has to say on the subject of bolting or welding, check out the ChatGPT article on Synthesis. AI writes really well, but certainly falls short in the “Good Technical Content” arena.
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