DIY Box Spanner




Introduction: DIY Box Spanner

About: Endeavouring to be a jack of all trades...

Each time I do an oil change on my van, I come across a bit of a struggle when changing the oil filter.

The reason is that the cap of the bowl in which the filter is, needs to be unscrewed (has a hex nut shape on the very top). Unfortunately, I haven't got a proper spanner for that job, and I either use an adjustable wrench or flat spanner, or both of them combined, since there isn't any space available in the engine bay, and I can't apply much strength to crack open the cap in the positions available.

Therefore, I decided to build my own spanner, dedicated for the job in question.

(which happens to be my first welding project)

Step 1: Needed:


-arc welder (bought a very old but good one for 40 euros)

-angle grinder

-other stuff (file, metal brush, hammer...)


-small metal plate but quite thick: 8mm (would probably work with thinner...but not under 5mm...depending on the application)

-metal tubes (a 20mm diameter tube, and a 25mm diameter one...around 40cm of each)

(All materials come from stuff at work that were supposed to be thrown away)

Step 2: Cutting a Stripe of Metal As a Chocolate Bar.

The first thing you want to do is to mesure the lenght of one side of the hex nut you need to make a spanner for.

Then you multiply by six (number of faces in the hex shape), to get the lenght of the metal stripe you need to cut.

I also recomment to add 6mm to that (which I didn't), so you don't struggle to much on adjusting in the next step.

The plate needs to be wider than the hight of the nut you're making the spanner for. (a few millimeters will be enough.

Once you have your dimensions, cut the stripe.

Then draw cutting lines to the lenght of one side of the hex nut. (That's when you would add a millimeter to it) You should have 6 equal sections.

Now you can cut on all these lines, at around 2/3 of the thickness of the stripe.

The result is a chocolate bar look alike metal stripe.

Step 3: Bending to the Hex Shape:

It would be most convinient at this step, to work with a quite hot stripe. (I didn't maintain a good temperature throughout the process, and haven't been able to bend it in one piece.)

Clamp the stripe over a solid edge, lined up with the cutting lines made earlier. One at a time.

Hammer down the section hanging out.

Check for angle match with a corresponding nut.

Repeat for each section.

As my stripe cooled down, the metal wasn't so bendy anymore, and it ended up breaking once I'd bended 3 sections. Which I ain't sure is a bad thing, since when I started to bend the fourth section, I had to grind a bit of metal of, inside the angles created, so that the nut fit nicely. (bending rounded the inside and I think that adding a millimeter to each section, or slightly more, can prevent the inside lenght to shrink to much).

So I ended up with 2 pieces of 3 faces each. (which might be the easiest way to do, rather than one piece that has to bent around the nut, as intended at first).

Make sure it wraps the nut nicely, but not to tight! (adjust by grinding of, if necessary)

Step 4: Welding the Hex Shape:

Now all you need to do is to weld the two pieces together. (I used 2.5mm welding rodes here)

And then, having checked if it still fits the nut, you can fill the cutting lines. (Used 3.2mm rodes)

Check again for fitment, because the heat created by the welding can moves things around.

(I double checked on the oil filter cap as well this time...(last picture))

Then grind the excess of, for a smooth looking shape.

Step 5: Welding It As a Box Spanner:

Once grinded, place it over the rest of your initial metal plate, and scrape the shape on it.

I opted for scraping the inside shape, and added a couple millimeters to that, but you could probably scrape the outside shape as well, and shade a couple millimeters of.

Then weld it on top of the previous piece. (2.5 and 3.2mm rodes)

(check again for fitment)

Step 6: Tube Welding:

Only now, this will become a tool.

I simply welded a tube on top that (which happened to be the right lenght for my one purpose only spanner...even though I could have used a couple centimeters more)

And then, after checking for the desired position on the van, I welded the handle bars on that first tube. (was a smaller diameter tube cut in 2 pieces)

I welded the handle bars at an angle, so that my hands had enough room to operate. (if welded at a 90* angle, my knuckles could have catched on the bonnet lock)

I could have welded the handle bar in one piece on top of the other tube, to over come that issue, but it turns out that the tube I used for the spanner, was at first, a tube that is very helpfull as an extension to crack some harsh nuts and bolts. So I needed to still be able to use it this way.

After a bit of grinding, and brushing, to make the overall look ok, I finished a can of black spray paint on it.

And that is it!

Step 7: Application:

This spanner I made is very purpose oriented.

It makes my oil filter change a real pleasure, and it stays in my van at all time, to be used as an extension when needed.

But I think that the way I built it can be applyed for many weird located nuts and bolts, or weird acces to them, that require a specific spanner, therefore, often very expensive ones!

This method is fairly easy (was my first welding project, and had only pratice my welds once before), quite quick to make (made it in about 3 hours, not counting the paint job), and pretty cheap (cost me none, but even if you need to buy the metal, there is not that much needed). So I will propably be making more of these in the future...

Hope you liked it, and I'd be pleased to see people make their own.


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    30 Discussions

    A bit... :) But only because it slipped of the pieces of wood at some point.

    With professional results I might add.

    No, he did not. He used a metal clamp, if you look carefully at the pictures

    Clever, but you probably could have purchased the tool for much less than you paid for the welder.

    3 replies

    First, there is no fun in buying if you can produce one. Sometimes when repairing stuff in the garage and suddenly realize that you need a tool wich you don't have, it always happens to be Friday 8 o'clock and all hardware stores are closed until Monday. Ebay needs a couple of days to deliver. So the best thing is to produce your own tools. Most of my tools are hand made by myself. I was very poor when I started young and hadn't the luxury of many people to afford new tools. So, thumbs up for this instructable!

    He already had the welder, and it's good practice.

    Not only is it cool that he made his own wrench, but it's actually useful, unlike a lot of stuff on Instructables. .

    This instructable ranks among the best I've seen. It's a real introduction to some practical metalworking and welding techniques and creative design. Excellent photos, too. (Picky point: I'd call the metal bar a strip.)

    Speaking to you as a very old and very retired welding inspector, pretty good for a first time welder. I see some undercut, caused probably from running too high an amperage setting and consequently having to advance too fast to get complete fill, some spatter and some lack of fusion. But for a beginner, you definately have potential. I'll sign off on your welds.

    1 reply

    Very nice of you to say! Thank you!

    Indeed, I didn't pay enough attention at first to the amperage settings. I'm starting to get the hang of it now, being more familiar with my welder.

    I recently had another issue, which you might have some tips for. A bunch of my rodes were unusable due to (I think) high humidity exposure. I tried to dry them out by placing them for many days, over my appartment's heaters, and for several hours on top of a halogen light. But it has not worked.

    Appart from putting them into the oven (which is not really appealing to me, because I cook in it, and therefore could be pretty unhealthy...?), would you have any suggestions for a recovery? Is it recoverable? (even though I realise that I should have been more careful on the storage...)

    Thanks again!

    Being a mechanic since the 70s, I have thousands of dollars invested in tools. So, I'd just use a socket, extension and ratchet. However, I also can appreciate well made tools and it looks like you did an excellent job building that one, looks professional enough to have a name brand on it!


    7 months ago

    Big thanks to everyone of you!

    I'm glad you like it!

    Definitely on the "cool" list. Figuring out how to do it is an accomplishment.

    Having the spanner end welded on is a benefit, too. Somewhere, there is a Ford truck with three of my 10mm sockets under the battery tray. When small tools disappear under the hood, they are gone forever. Lesson: use electrical tape or masking tape to hold the socket on the extension.

    A few weeks after my grandfather had some repair work done, I checked the oil in his car. I found the service shop had left a 32mm box wrench about 40cm long. Knowing what it cost, I took it back to them. I can't imagine how you could miss seeing something that big while picking up your tools.

    1 reply

    First working as a mech and the boss was using my tools and kept dropping them on the floor. "Hay what the hell thats my tool on the floor" He said " If on the floor the do not drive away" from that time I always drop them the floor. Note they were Snap On's A full tool box after 30 plus years of wrenching

    nice job. I might make one of these but to take off the chrome lug nut covers on larger trucks. Would of saved me time messing around with large pliers to get them loosened.

    Excellent idea... thanks

    awesome, great job


    7 months ago

    A great idea & brilliant bit of craftsmanship!

    Thanks for posting.,,,,,,,,,,