Tool tip: My pin-head method for making a special size allen (hex) key wrench

Today I was working on a project and discovered I needed a 5/16" allen (hex) key wrench to continue. I looked through what I had in the toolcase, and all the sets stopped at 7/32" as the largest size. Well, there was one oddball set I had that had a 1/4" hex key, but that was the biggest. I needed a 5/16". Sigh. I did have a few that were bigger, but they were much bigger. For xmission drain plugs and the like. But no 5/16".

I looked at Harbor Freight website, there’s a retail outlet of theirs nearby, but according to their website, they didn’t have any 5/16" hex keys in any of their sets either. 5/16" hex keys are availble from other vendors, but I’d either have to go to a different tool store, none near by, or buy one on the internet.

So here’s what I did. I found a 5/16" bolt and two nuts. The 6 sided head of the bolt fits exactly. I put the two nuts on together on the end, then tightened them against each other, so they are locked together. I think this technique is called a “jam nut”.

Anyway, then I put the head of the bolt into what I wanted to remove, and used a wrench on the two jammed nuts to twist the bolt, and, voila, it worked like a charm!

What I needed to remove with the 5/16" hex key didn’t require much force to free. Because I was untightening, this might not work if you need to remove something that is really stuck. In a pinch – if you had a welder – you could probably weld the two nuts to the bolt and then it would be good and strong.

Anybody have other solutions to this problem, needing a hex key of some size, and not having it, so you make it yourself?

Is there a better method, other than welding, so the un-tightening doesn’t cause the “jam nut” double-nuts to become unlocked?

Nice solution, @GeorgeSanJose.

What project was it that required a “SAE” allen wrench? Big pet peeve of mine: I realize there’s enough of a “legacy” around wrenches/socket wrenches that you’re stuck with inch measures, but for a tool made popular after metric became common, why bother with the duplication of effort?

Thank goodness Torx demarcated their tools in “sizes” (without admitting they’re based on metric dimensions) or surely somebody would kvetch about “why do we have to use these dag gum ‘foriegn’ Torx-heads!”

I’ll have to remember that. I had a similar fix years ago when the aftermarket pulley for my a/c loosened. I could either fix it the right way by removing the harmonic balancer (it was bolted to the rear) or use two nuts (jammed) on the bolt threads sticking out the front. I did that, tightened the bolt, then used one of the jam nuts to lock the bolt to the balancer. Stayed tight for 7 years (until it was junked).

It was a plumbing project @meanjoe75fan. Plumbing stuff still is mostly in SAE dimensions.

I understand your pet peeve completely. I’ve never really understood the SAE/Metric tool situation we’ve got or how we got it. It seem to me we should either decide to have all one, or all the other. What we got now, both, is the worst of all possible worlds; we fix-it types have to have two sets of each hand tool for fasteners and the like, one SAE, and one metric. Sigh.

It’s odd that you could not find a 5/16" Allen wrench at Harbor Freight. It’s a very common size. In fact, I have this set of Allen wrenches at work, and it includes a 5/16" wrench: Your method of making a tool to substitute for an Allen wrench is brilliant. I actually have one of those in my toolbox at work. We have plastic granulators that need maintenance on a regular basis, and opening some models of them requires a 22mm Allen wrench or socket, which can be difficult to find and expensive to buy. Nobody wants to order sockets from Grainger and pay their prices, so many of us have taken a 1/2" NC bolt and two nuts (I think it’s 1/2" NC anyway, don’t remember for sure), jammed the nuts together, and use it with a 7/8" socket and ratchet to open these granulators. 7/8" is close enough to 22mm to work for this task, so that is what we do to save money.

To keep nuts from loosening, install enough of them to reach the end of the threads or stack a bunch of washers on the bolt. After you do that you will never again need my advice!

@GeorgeSanJose, that method you describe is how I removed the oil galley plugs on my Supra. It was posted on a Supra forum, and worked like a charm. The only difference was using Metric. As far as the jam nuts, to loosen, use a wrench on the lower nut, as loosening the plug will tighten the jam nut against the upper nut. Use the upper nut to tighten the plug back down.

An alternative would have been a 5/16" “coupling nut”.

Anyway, nice job.

Thanks for the comments. Yes, I realize now it won’t loosen if I keep the wrench completely off the upper nut, thank to @BustedKnuckles for pointing that out. @mark9207 … yes, you are right, 5/16" is a common hex key size and Harbor Freight has them. And I had one. I messed up the dimensions in my post. I had 5/16" on the brain I guess. I meant that I needed a hex key sized the same as the head size of a 5/16" bolt, which fits a 1/2" wrench. I needed a 1/2" hex key. The biggest hex key I had was 3/8". It’s interesting to see how everbody adapts to these kinds of little mechanical difficulties. A lot of inventive folks here.

1/2" is definitely a less common size. I actually use one at work all the time. When I bought it for work, I got it at Sears. It was a Craftsman and I believe it cost $20 (ouch). For the last few years, work has been providing them since they do wear out with use. When I wore out my Craftsman, I kept the replacement at home and use the one I was issued at work. It has since been replaced once or twice. The nut and bolt trick wouldn’t work for such heavy, frequent use.

Good to know Sears has 1/2 hex keys. I tried the 1/2" drive on my socket ratchet first, but it is square & didn’t fit the 6-sided hole. I wonder why the hex key sets don’t go to 1/2" as a common thing? I’ve had this problem before now that I think about it, in a different application. For that I think I just wrapped some duct tape around my 3/8" hex key, until it was about 1/2", and it worked pretty good actually.

A stud remover and a bolt with a half inch head. It works better if you already have a stud remover. Thirty dollars if you don’t.

You can get Craftsman tools at Ace Hardware, Summit Racing, and Orchard Supply Hardware in addition to K-Mart and Sears.

Also, after my “rant” about SAE allen wrenches, it occurred to me: 8mm is almost exactly 5/16". If you have a metric 8mm, you’re good.

@meanjoe75fan, @GeorgeSanJose later said that he used 2 nuts that fit on a 5/16" thread and that the hex nuts were 1/2". But that’s pretty close to 13-mm (actually 12.7-mm).

Yes, 13 mm would probably have worked, but the common hex key sets end at 10 mm as the largest.

I did the reverse of that once. I did a little body work on a friends Mark and needed to adjust the headlights. It was a hex bolt. I went to the hardware store and the guy scratched his head for a second and came up with an allen bolt that fit it and a couple nuts. Worked fine for one time needed. Wish I would have thought of it myself.

BTW, I saw more than one T-handle set at the Sears web site that included a half inch hex key.

Good idea @Bing. A short allen bolt (aka socket-head screws), 2 nuts, and a combo wrench might prove a useful technique when access to the head of the bolt is a problem. Or you just don’t have that dimension of socket.