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Old 25th Feb 2021, 6:16 pm   #1
OldTechFan96
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Default What Allen Key Size?

I'm trying to remove a grub screw on a piece of test gear and I don't know what size it is or whether it is Imperial or metric.

2mm is too big and 1.5mm is a bit too small. The piece of gear is from the '70s.

Does anybody know the correct size?

Thanks
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Old 25th Feb 2021, 7:01 pm   #2
turretslug
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Default Re: What Allen Key Size?

Could it possibly be 1/16" (approximately 1.59mm)?

I've often found that small, cheap (in particular) Allen keys can be a bit vague and prone to tolerance as to size, sometimes it's necessary to try a few different makes of what claims to be the same size to find one that is a comfortable fit and won't slip round and mash up the profile of either key or fastener.

It looks like a hex key fitting from the pic, but sometimes alternative types turn up, like Bristo spline- I was intrigued to find that the tiny aerial trimmer knob of a WW2 US receiver was retained by a titchy grub screw with something like a four-spline version of a Bristo fitting, but with a Maltese cross profile. What would one ask for there?!
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Old 25th Feb 2021, 7:02 pm   #3
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Default Re: What Allen Key Size?

Possibly imperial 1/16 inch. I would try cleaning the muck out of the socket as that will stop the key going in properly and encourage rounding of the hex.
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Old 25th Feb 2021, 7:12 pm   #4
The Philpott
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Default Re: What Allen Key Size?

With lower quality allen keys sometimes the ends look badly sheared off like a piece of licorice, have a close look before using it. It can be remedied with large ones by grinding, but these smaller ones are best discarded.

Dave
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Old 25th Feb 2021, 8:01 pm   #5
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Default Re: What Allen Key Size?

Looks to be a Farnell oscillator, possibly an LF1, maybe that will help with identifying the grub screw Allen key size.

David
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Old 25th Feb 2021, 9:45 pm   #6
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Default Re: What Allen Key Size?

Quote:
Originally Posted by factory View Post
Looks to be a Farnell oscillator, possibly an LF1, maybe that will help with identifying the grub screw Allen key size.

David
Correct!

I had a similar issue with an early 60's Marconi O/P meter that must have used the same Allen head. I 'cheated' and used a similar sized Torx bit. This might not work with the Farnell as the bit is recessed.

1/16'' or 1.59mm could be right.
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Old 26th Feb 2021, 1:23 am   #7
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Default Re: What Allen Key Size?

Are you sure it is Hex and not Torx? A few years ago I bought a miniature 10-turn pot and its knob, which was supplied with a Hex Allen key. It was impossible to tighten and it turned out that the grub screw (0-80 UNF) had a Torx socket recess.
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Old 26th Feb 2021, 5:00 am   #8
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Default Re: What Allen Key Size?

And are you sure that was Torx? I have a piece of equipment (Trend TDMG2C teleprinter test signal generator thing) with a 10 turn pot and dial. The grub screw in that takes a Bristol Spline tool.
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Old 26th Feb 2021, 1:15 pm   #9
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Default Re: What Allen Key Size?

Quote:
Originally Posted by OldTechFan96 View Post
Quote:
Originally Posted by factory View Post
Looks to be a Farnell oscillator, possibly an LF1, maybe that will help with identifying the grub screw Allen key size.

David
Correct!

I had a similar issue with an early 60's Marconi O/P meter that must have used the same Allen head. I 'cheated' and used a similar sized Torx bit. This might not work with the Farnell as the bit is recessed.

1/16'' or 1.59mm could be right.
I've checked my Farnell FG1 with some Allen branded sets, the 1/16" fits perfectly, but the 1.5mm from the metric set is too loose.

David
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Old 26th Feb 2021, 1:27 pm   #10
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Default Re: What Allen Key Size?

Thanks for confirming the Allen head size. Wilco sell a handy Imperial and metric set that includes a 1/16" key.
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Old 26th Feb 2021, 1:33 pm   #11
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Default Re: What Allen Key Size?

I had downloaded the manufacturer's technical data sheet for the knob, which stated that the grub screw was Torx. With such a small size it was difficult to see with the naked eye. The distributor sent another unit as the splines of the original had been damaged by my attempts to tighten it with the hex key they had supplied, and small unified grub screws are not exactly off the shelf items in the UK.
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Old 26th Feb 2021, 1:56 pm   #12
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Default Re: What Allen Key Size?

Quote:
Originally Posted by emeritus View Post
I had downloaded the manufacturer's technical data sheet for the knob, which stated that the grub screw was Torx. With such a small size it was difficult to see with the naked eye. The distributor sent another unit as the splines of the original had been damaged by my attempts to tighten it with the hex key they had supplied, and small unified grub screws are not exactly off the shelf items in the UK.
Accu have 0-80 UNF grub screws in various lengths with an Allen hex of 0.028"

David
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Old 26th Feb 2021, 8:01 pm   #13
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Default Re: What Allen Key Size?

Comments have been made about accuracy of low quality Allen keys. Your photo shows "Rolson", one of the really cheap purveyors of every sort of rubbish, from timing guns (useless) to, well, Allen keys. Try some by one of the USA tool manufacturers, or even a (genuine) UK manufacturer, if you can find one.
Les.
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Old 26th Feb 2021, 8:29 pm   #14
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Default Re: What Allen Key Size?

I agree with Les and I'd reconsider purchasing the cheap Wilco set. Bondhus (US company) is considered by some to be one of the best. Worth spending a few pounds more for decent quality. For example:

https://www.ebay.co.uk/itm/Bondhus-9...MAAOSwokNgNkuL

Alan
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Old 26th Feb 2021, 10:56 pm   #15
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Default Re: What Allen Key Size?

Quote:
Originally Posted by OldTechFan96 View Post
Quote:
Originally Posted by factory View Post
Looks to be a Farnell oscillator, possibly an LF1, maybe that will help with identifying the grub screw Allen key size.

David
Correct!

I had a similar issue with an early 60's Marconi O/P meter that must have used the same Allen head. I 'cheated' and used a similar sized Torx bit. This might not work with the Farnell as the bit is recessed.

1/16'' or 1.59mm could be right.

Interesting Metric set in the picture- it has a stray imperial key in it. 1.27mm aka 1/20" or 50 thou. Often found on small knob grubscrews!
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Old 27th Feb 2021, 10:58 am   #16
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Default Re: What Allen Key Size?

Many years ago, in the early 60's, to supplement a lowly airman's wage, I ran a wee stall in Paddies' Market, Liverpool,(off Casnau Street nr. Scotland Road), on a Saturday. Before it opened, stall-holders would poke about in each other's junk & cherry-pick wee bargains. My wee bargain was a tobacco tin full of small to medium imp. Allen Keys. They were of the best quality & still in regular use today. I've since seen modern cheapo Allen keys & guess that some are just mild steel as the flats wear very easily.
As a tip regarding loosening reluctant grub-screws :- insert a gash or worn cheapo allen key, then briefly heat it(& hence the grub-screw, but not the plastic or bakelite knob) with a soldering iron. As it cools, drop in a wee dose of "looseoil" or WD40. This enhances the lubricant being drawn right into the tight grub-screw/knob's thread. Then proceed with a decent allen key after a minute or two's cooling time.

Regards, David
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Old 27th Feb 2021, 11:16 am   #17
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Default Re: What Allen Key Size?

My set of metric Allen keys are the real thing, having actually been made by the Allen company. Bought from a long defunct local shop that used to carry an excellent range of quality precision tools and fasteners.

Until it moved to Wales in the 1990's, the Patent Office's Classification Section used to have a little-publicised free service in which one of their examiner's official duties included answering enquiries from the public. If he didn't know the answer himsef he would ask an examiner responsible for the relevant technology. They had files covering the most popular questions, and always had bursts of enquiries when competitions were being run in magazines. The most popular query from men was "Who invented the Allen key?", and from women "Who invented the brassiere?". (The Allen key was never patented.)

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Old 27th Feb 2021, 12:09 pm   #18
barrymagrec
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Default Re: What Allen Key Size?

Unbrako always used to be the name to go for, both for allen keys and allen screws and bolts.
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Old 27th Feb 2021, 12:20 pm   #19
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Default Re: What Allen Key Size?

I recently needed a set of small Allen keys and got these:

https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

They have been useful for small Allen key grubscrews and seem good quality.
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Old 27th Feb 2021, 1:42 pm   #20
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Default Re: What Allen Key Size?

Quote:
Originally Posted by Herald1360 View Post
Interesting Metric set in the picture- it has a stray imperial key in it. 1.27mm aka 1/20" or 50 thou. Often found on small knob grubscrews!
I have an idea that the 3 smallest (common?) sized Allen keys, 28 thou, 35 thou and 50 thou are actually the same in the imperial and metric sets. But that doesn't stop one tool company having separate part numbers for the 1.27mm and 50 thou tools.

As an aside I find it amusing that many sets of 'metric' feeler gauges have 0.38mm and 0.635mm blades. Better known as 15 thou and 25 thou.
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