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Old 12th Jul 2021, 4:42 pm   #1
6AL5W-Martin
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Default Imperial Allen key sizes?

hello from the metric germany

I want to buy a really complete set of imperial allen keys,
useful for all american and UK radios and test gears.

My special question about that:

one german company offers them all seperate, and the smallest allen key there seems to be a 3/64. They have NOT the little allen key named "fifty tou", written as .050 in american sets, seen on amazon.
All this american sets of allen key have the .050 but NOT the 3/64.

So i need to know: is the 3/64 identical with the .050 ?
If not I have to buy the american set, additional the 3/64 from the german.

Martin
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Old 12th Jul 2021, 5:12 pm   #2
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Default Re: imperial allen key sizes

3 /64 is 0.046875 so not quite the same.

but 1.27mm is and theyre available on ebay.....
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Old 12th Jul 2021, 5:16 pm   #3
The Philpott
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Default Re: imperial allen key sizes

3/64" equals a very small amount under 47 thou (0.047") so i would HOPE that would be close enough....or they could actually be identical.

Oddly, the metric system was invented by a Brit!

(Edit- Yes, 1.27mm does equal 0.050" !)

Dave
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Old 12th Jul 2021, 5:28 pm   #4
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Default Re: imperial allen key sizes

This set contains both a 0.050" and a 3/64" so no, not the same.

https://www.ebay.co.uk/itm/5PCS-Hex-...-/153299046207

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Old 12th Jul 2021, 6:46 pm   #5
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Default Re: Imperial Allen key sizes?

It's essential to have the right size Allen key.

Just a smidgen wrong, and (particularly when unscrewing a tight screw) you risk rounding-off the hexagon in the screw - and then you'll never get it out.
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Old 12th Jul 2021, 7:29 pm   #6
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Default Re: Imperial Allen key sizes?

Not all US stuff uses Hex, some uses Torx. A few years ago I bought a small American-manufactured Bournes 10-turn pot and dial from a UK distributor. The dial was supplied with a very small Allen key for the dial's 0-80 UNF grub screw, but it wouldn't tighten it. On checking a data sheet on the manufacturer's web site, it turned out that the dial's grub screw had a Torx recess and not a Hex. The distributor duly supplied a replacement dial with the correct key, as the original grub screw's recess had become damaged by my attempts to tighten it. Being right down inside the knob and such a small size, the different shape of the recess was not obvious until I used a torch and a jeweller's loupe.

Last edited by emeritus; 12th Jul 2021 at 7:41 pm. Reason: typos
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Old 12th Jul 2021, 7:36 pm   #7
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Default Re: Imperial Allen key sizes?

I would reiterate that it's really important to have exactly the right sizes for these small allen keys. 3/64" is not the same as 0.050". I have imperial allen keys for working on US-designed equipment (mostly Tektronix) and I have to import them from the UK because imperial tools are next to unobtainable here in Poland. The 0.050" gets quite a lot of use, together with the next size up (1/16" I think).

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Old 12th Jul 2021, 8:32 pm   #8
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Default Re: Imperial Allen key sizes?

I agree with Kalee and Chris; it's vital to have the exact one when they are really tight.

I have an imperial set and a matching metric set bought in the US from Craftsman tools - just love them!

I've had to find some smaller keys for specific jobs and have done well by going to model-makers shops.

B
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Old 13th Jul 2021, 12:10 am   #9
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Default Re: Imperial Allen key sizes?

Some American equipment uses a non-hexagonal key called "Bristol Spline" in fairly small sizes. Without looking carefully, they are easily mistaken for hexes

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Old 13th Jul 2021, 3:17 am   #10
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Default Re: Imperial Allen key sizes?

I've certainly come across Bristol spline grub screws in knobs and turn-counter dials -- on British equipment. The keys to fit them are not that easy to find but they do exist.

Never seen a 3/64" Allen key though. There are even smaller ones, 28 thou and 35 thou which I do have (and have used), I have an idea that there are metric ones exactly the same size in some sets. For some odd reason, one of my tool sets contains identical 50 thou and 1.27mm Allen key blades _with different part numbers_. Go figure.
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Old 13th Jul 2021, 3:24 am   #11
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Default Re: imperial allen key sizes

Quote:
Originally Posted by The Philpott View Post
3/64" equals a very small amount under 47 thou (0.047") so i would HOPE that would be close enough....or they could actually be identical.

Oddly, the metric system was invented by a Brit!

(Edit- Yes, 1.27mm does equal 0.050" !)

Dave
Could be our education system, but I thought the metric system belongs to one Napoleon Bonaparte.
You can shoot me down if I am wrong, but I have won many trivia contests knowing that one.
I DO detect you say "invented" not "introduced"

With respect
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Old 13th Jul 2021, 3:29 am   #12
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Default Re: Imperial Allen key sizes?

The first practical realisation of the metric system came in 1799, during the French Revolution, after the existing system of measures had become impractical for trade, and was replaced by a decimal system based on the kilogram and the metre. The basic units were taken from the natural world. The unit of length, the metre, was based on the dimensions of the Earth, and the unit of mass, the kilogram, was based on the mass of a volume of water of one litre (a cubic decimetre). Reference copies for both units were manufactured in platinum and remained the standards of measure for the next 90 years. After a period of reversion to the mesures usuelles due to unpopularity of the metric system, the metrication of France and much of Europe was complete by the 1850s.

A quote from the Wikipedia, which I pay for every year.

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Old 13th Jul 2021, 7:07 am   #13
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Default Re: Imperial Allen key sizes?

Quote:
identical 50 thou and 1.27mm Allen key blades _with different part numbers
I have a metric/imperial adjustable spanner one side it's 6" the other 150mm Sensibly both sides have the same part number.
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Old 13th Jul 2021, 10:29 am   #14
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Default Re: Imperial Allen key sizes?

I have an old physics textbook that has a historical introduction setting out the development of the science. It includes some direct quotations from the works of early scientists. Apparently Sir Isaac Newton and his English contemporaries normally used French units of measurement, such as the Paris Foot and the Toise, reflecting the high status of French science before the revolutonaries executed or expelled many of their scientists for being elitist. Weights and measures were not standardised throughout Britain at that time. Different towns had their own standards until the use of imperial standards was made mandatory in Victorian times, although (no doubt due to Prince Albert's influence) metric standards were also legalised for alternative use for many purposes, but seldom used in everyday commerce).

Last edited by emeritus; 13th Jul 2021 at 10:38 am.
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Old 13th Jul 2021, 6:02 pm   #15
6AL5W-Martin
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Default Re: Imperial Allen key sizes?

great help here, thank you all.

I need that
Bristol spline + complete set imperial alan keys, for boatanchor radio + Tek knobs.
metric is complete here.
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Old 17th Jul 2021, 9:03 pm   #16
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Default Re: Imperial Allen key sizes?

It is a very good idea to have imperial as well as metric Allen keys at hand. Several times I have had problematic screws with rounded edges: If the "matching" metric key gets no grip any more, try the closed imperial size and vice versa! With a little help from a small mallet most but all screws cannot withstand that treatment.

Joe
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Old 17th Jul 2021, 9:17 pm   #17
The Philpott
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Default Re: Imperial Allen key sizes?

-Sounds like i've soaked up some metric misinformation from one of the documentary channels, either Quest, Dave or Yesterday most likely!

I have a victorian book of tables of measurement somewhere, it's hilarious. Three different types of ounce, Firkins, Tuns, Kilderkins, Bushels etc. A whole different world.

Dave
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Old 23rd Jul 2021, 7:04 pm   #18
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Default Re: Imperial Allen key sizes?

I don't for one moment believe that the Kilogram was the original base measurement, and the gram derived from it!
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Old 23rd Jul 2021, 10:55 pm   #19
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Default Re: Imperial Allen key sizes?

You are perfectly correct.

The following is an extract from the "Historical background of definitive units" part of a paper delivered at a meeting of the International Union of Pure and Applied Physics, Chicago, 24th June 1933:

" 1799. The meter and kilogram in platinum were definitely fixed and defined as the standards of length and weight by the French statute of December 10, 1799. This retained the gram of the provisional statute of 1795 as the basis of the nomenclature but substituted the kilogram as the physical standard. This inconsistency in nomenclature has continued to the present time. The definitive system gives the kilogram a factor-free name for optional use. "

[At the time there was a proposal, never pursued, to rename the kilogram to eliminate the "kilo" decimal multiplier from the base unit of the proposed "definitive" system, essentially the MKS system].

This thread prompted me to check the sizes of the Draper combined metric and imperial allen key set I have had for several years. I found that what ought to be the 1/8" key, is in fact a second 7/64" key. Fortunately I do have a 1/8" key in my old dad's baccy tin of assorted Allen keys, should I ever need one.

Last edited by emeritus; 23rd Jul 2021 at 11:13 pm. Reason: typos
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Old 28th Jul 2021, 2:23 am   #20
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Default Re: Imperial Allen key sizes?

Metric (red) Imperial (yellow) plus a few of the small imperial sizes as they are the ones that wear out first. Bought from the Snap-On van man at least 15 years ago - reasonably expensive but they have lasted well.
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