Trouble with Allen Wrenches

[Calandrod]

I’m having trouble finding the right size for the set screw. After spending extensive time turning this flywheel, machining the set screw down, and then drilling and tapping a hole for it, I discovered I don’t actually have an Allen wrench that fits it.
It’s between a 1/16 and a 5/64.
1/16 was barely too small and 5/64 was a little too big. It’s a 6-32 so I don’t think it would be metric. It seems as though all the tiny sets I’ve been looking at don’t have anything in between those sizes. Anyone have an idea of what size I’d need and where to find it?

 

[extropic]

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.

 

[GrifterGuru]

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.

There is a small chance you have a Bristol drive set screw

@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.

 

[Be_Zero_Be]

The first law of Allen Wrenches :
The first one you try is too big.
The second one you try is too small.
The correct one is missing.

 

[GrifterGuru]

The first law of Allen Wrenches :
The first one you try is too big.
The second one you try is too small.
The correct one is missing.

@Be_Zero_Be

That should read:

" The first law of All Tools "

 

[GeneT45]

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

 

[WobblyHand]

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.

 

[cathead]

It's all about fit. I keep all my Allen wrenches in a jumbled configuration and use the trial and error method.
Maybe it seems disorganized with American and Metric in the same drawer but rarely find one that wont work.
This country is slowly gravitating to metric as time goes on it seems.

 

[markba633csi]

Could be metric

 

[mmcmdl]

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.

+ 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 .