Trouble with Allen Wrenches

[Calandrod]

I assume you are correct in stating that you tapped the hole 6-32.
6-32 socket set screws use 1/16" hex keys.
.8mm pitch is 31.75 TPI and 3.5mm= .1378", so such a metric set screw could easily be mistaken for a 6-32 (#6 major diameter=.138").
So a 3.5mm-.8mm pitch setscrew could easily be mistaken for a 6-32.
However 3.5mm-.8mm pitch doesn't seem to be a common size. McMaster sells that size in SHCSs, but not in set screws.
Also, there is no standard hex key (inch or metric) between the sizes you mention.

My recommendation is to try a different set screw.

Take a look at the troublesome set screw under some magnification to get a better look at the socket. There is a small chance you have a Bristol drive set screw. Very rare and I would segregate it and clearly label, or throw it away.

Let us know how it works out.

@extropic thanks for the recommendations. I tried a different screw and it had the same issue. The screws came from a pretty organized bin so I am fairly confident it is the correct one. Also it fit the 6-32 tap pretty easily and I don’t think it cross threaded.I’m ordering a new set of wrenches to try them next.

Allen keys are measured A/F (Across flats).

Do you have any way to get an internal measurement betweens flats, such as test pins?

It being between 0.0625" and 0.0781" puts it between 1.54mm and 1.96mm.



@extropic

You mean one of these? That are/were used on PHI optics as well as military radios, avionics, and test equipment applications?
I did not even know McMasterCarr sold the keys until I looked at potential sources for them.

View attachment 506560

@GrifterGuru good thought. I’ll take a look at that if the new wrenches don’t solve it.

It should be mentioned that there are plenty of off-size hex wrenches AND hardware out there (though the hardware is generally oversized when it's off). If you're using wrenches or fasteners of questionable quality I'd recommend immediately replacing them. That may solve the problem by itself, but even if it doesn't, you'll have some good wrenches...

GsT

@GeneT45 thanks! I didn’t even consider that. I ordered a new set of Bondhus wrenches today to try that (previously I had a pair of Chinese ones for small stuff like this).

I've found that cheaper sets of Allen keys are not true to size. Get yourself some decent ones. They are not expensive. Using a proper fitting key makes a big difference. Some of the conneseurs here can recommend some high end ones, but I have found Bondhus and Chapman to be very serviceable. Bondhus sets can be purchased inexpensively. The Chapman sets include interchangeable bits including screw driver bits and a neat mini ratchet for stubborn situations. I've had both sets for decades now. Good tools last.

@WobblyHand I appreciate the info and help. I ordered a set of Bondhus ones that should come this week and I want to look into those Chapmans a little further. I’m all about quality and long term tools.

+ 1 on the Chapman sets . They've lived in my top drawer since 1999 .

Most likely the set screw is bad . I've run across bad ones over the years and just toss them .

You can also taper grind the oversize wrench to fit that screw if you need to , kind of like a " sock it out " tool . Or just buy a set , and use a tap wrench to tighten .
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@mmcmdl I hadn’t considered that until you guys mentioned it but I tried a second set screw and it had the same issue so I’m thinking it’s the wrench. Hopefully a quality set will resolve it! Also I love the improvising idea; hadn’t thought of that one.

For a good portion of my career I used Allen wrenches on a daily basis in a production environment. The absolute best I ever had were made by Unbrako ( https://unbrako.com/wrenches )
I have a few that have been twisted so hard they look like a barber pole and I don't remember ever having one break.

Ted

@talvare I looked for those and couldn’t find any new sets for sale. Where have you ordered them?

OP, are you sure the 1/16 set screw isn't wallowed out? That would make the Allen key seem too small.

Rick "hoping that's not the problem" Denney

@rwdenney good thought. I checked it against another screw and no fit. I think it’s the Chinese crappy wrenches I had. I’ll know soon.

That "should" be a 1/16 allen wrench. But there are issues....

The tolerance of the screw MIGHT be spot on. it MIGHT be sloppy. It MIGHT have a metric drive size on an SAE thread.
I have no idea where your screw came from, or if it's got any kind of pedigree....

The tolerance of your wrench MIGHT be spot on. It Might be sloppy. It MIGHT be worn some. It MIGHT have certain sizes purposely out of spec because you can "squeak by" on some metric sizes...

If your set includes an 0.050 key, double check that you havn't stuck the two (that and the 1/16) in the wrong slots,s

Bottom line, get out your measuring tools.... If it doesn't work properly (which on stuff that small will still be "weak" feeling, and will strip right out if you yarn on it too hard. The torque on a screw that size not much....), but if it doesnt' work properly, SOMEBODY's dimensions are off...

With hex keys, the TOOL is smaller to dead on. a 1/16 key should be 0.0615 (sloppy) to 0.0625 (abnoxiously tight). The socket is larger to dead on. In this case, 0.0625 to 0.0635.

@Jake M thanks for the advice! Really great insights.

 

[extropic]

There is such a thing as a 1.5mm hex key.
1/16" = .06250"
1.5mm = .05906"

Maybe you were mistakenly using a 1.5mm hex key instead of a 1/16".

Did you mike the key?

The decimal inch sizes I showed above are nominal to 5 decimal places. It wouldn't surprise me if the keys are a couple of mills smaller than nominal.

 

[fixit]

The socket may have cracked in the screw. It happened to me one time. Then I could fine no wrench that would fit.

 

[talvare]

"@talvare I looked for those and couldn’t find any new sets for sale. Where have you ordered them?"

Well, I haven't purchased any in quite a few years, but after looking on the internet, it almost seems like they aren't making the Allen keys any longer and it appears that their main product is fasteners. I did see some used sets for sale on eBay, but other than that, I guess I led you on a wild goose chase. It's too bad, they were an excellent tool.

Ted

 

[GeneT45]

"@talvare I looked for those and couldn’t find any new sets for sale. Where have you ordered them?"

Well, I haven't purchased any in quite a few years, but after looking on the internet, it almost seems like they aren't making the Allen keys any longer and it appears that their main product is fasteners. I did see some used sets for sale on eBay, but other than that, I guess I led you on a wild goose chase. It's too bad, they were an excellent tool.

Ted

Some other good brands are Eight and Wiha. Wiha tools just started showing up at Lowe's though, and that usually bodes poorly for sustained quality as the big box stores flog their suppliers endlessly for lower prices.

GsT

 

[mmcmdl]

Good lord . Unbrakos sell for the price of gold on fleapay .

 

[Calandrod]

Figured it out! All I needed was a nice quality set of wrenches. I order the Bondhus set and it fit tightly and perfectly. I really appreciate the help! Thanks guys.

 

[GrifterGuru]

Figured it out! All I needed was a nice quality set of wrenches. I order the Bondhus set and it fit tightly and perfectly. I really appreciate the help! Thanks guys.

Funny, I just ordered a set of Metric and Imperial Bondhus T-Handle allen (hex) keys!

Fed up of the "el-cheapo" Sealey brand ones I have been using as a stop-gap.

Might have to invest in a smaller "nested" set of each too..