Odd size die

[John MCParticipant @johnmc39344]

While looking through my box of spare metric taps and dies I came across this die. I assumed it was metric, M4 x 0.7, standard coarse metric. Its not, the only thread that will screw in to it is 3/16" BSF. It fits the screw nicely, seems an odd way to annotate a die.

Any thoughts?

John

[John MCParticipant @johnmc39344]

[Brian HParticipant @brianh50089]

Very odd one; 4.7mm is 0.185 ins which is very close to 3/16"

Having worked in the Aircraft Industry I did wonder if AGS stood for Aircraft General Standard which was the common designation for all aircraft fasteners but that would not apply to tooling.

I hope that someone can come up with an explanation.

Brian

[Michael GilliganParticipant @michaelgilligan61133]

This is possibly the most comprehensive list of thread sizes readily available: **LINK**

http://pages.cs.wisc.edu/~bolo/workshop/thread.html

2BA would seem the obvious answer, but there are threads either side of that which are very close.

MichaelG.

[old martParticipant @oldmart]

The numbers don't make much sense, M5 is very close to 3/16 BSF, very slightly bigger, 0.197" as compared to 0.1875". Perhaps it is one of those old proprietary threads used to stop unauthorised repairs or something from the firearms industry.

[Bo’sunParticipant @bosun58570]

A "security" thread as mentioned, or maybe something to protect a design/patent seems plausible.

[JasonBModerator @jasonb]

It's almost a bicycle thread as they are listed the metric diameter of imperial nominal sizes such as FG6.35 is a 1/4" thread but surprised that there is a jump between 2.4 and 6.35 with no 1/8" or 3/16" sizes listed. Though at the time I expect they used the imperial sizing rather than the metric that is now shown in the DIN spec

Size and pitch also ties in with CEI where the 3/16" nominal is 32tpi the same as BSF

[Michael GilliganParticipant @michaelgilligan61133]

I have no idea whether this is relevant, but

A.G.S. stands for [stood for] Aircraft General Standard

**LINK**

AGS Parts

MichaelG.

[JasonBModerator @jasonb]

Did you see that in Brian's post?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 30/04/2020 08:56:10:

Did you see that in Brian's post?

.

Quite evidently not

I was focussed upon my own assumption that the die is probably 2BA by another name.

mea culpa

MichaelG.

[Clive FosterParticipant @clivefoster55965]

+1 for it being a motorcycle spoke thread size die. Spoke threads are rolled and the actual thread diameter is always a bit larger than the spoke itself, which is sized by nominal wire gauge anyway. Then, back in the day, galvanised to add yet another layer of confusion. The odd old ones I've measured never seem to come up the size they ought to!

Couple of links to modern sources of data here :- **LINK** and **LINK** . But these are modern equivalents. Back in the British bike mass production days spokes were a specialist item with their own special sizes subtly different from normal sizes. Presumably to reduce the chance of folk using ordinary materials for replacements which would not be up to the loading.

If it is a spoke die no way would it actually cut a thread on a spoke. Purely for cleaning up.

Clive

[John MCParticipant @johnmc39344]

Thanks for the replies. I've cut a thread with the die. Not as straight forward as I hoped, the OD of the die is 24mm. A clue to its use?

I checked the thread with a gauge, definitely not 3/16 BSF, although a nut will screw on. Same for 2BA, closer than the BSF though.

I don't think its a spoke thread, as Clive F. says they are rolled, having said that I have a few dies for spoke threads, I assumed for cleaning up as Clive says.

Still a mystery, the die has gone in the "odd taps and Dies" box along with and a 1/4" x 25 tap, amongst others.

John

[Michael GilliganParticipant @michaelgilligan61133]

I remain convinced that it is most likely to be 2BA, John

… I am aware of nothing else for which 4.7 is directly relevant.

MichaelG.

[Paul RhodesParticipant @paulrhodes20292]

Looking at the original picture I can convince myself that the "4" is followed by a poorly stamped fraction.

Certainly there appears an"R " in the lower left which must strike a chord with some of the experts on here.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Paul Rhodes on 01/05/2020 14:03:33:

[…]

Certainly there appears an"R " in the lower left which must strike a chord with some of the experts on here.

.

… probably stands for Right hand thread

Turnbuckles and similar devices would use Left and Right, so it’s convenient to have them marked.

MichaelG.

[John MCParticipant @johnmc39344]

Posted by Michael Gilligan on 01/05/2020 12:41:36:

I remain convinced that it is most likely to be 2BA, John

… I am aware of nothing else for which 4.7 is directly relevant.

MichaelG.

My 2BA thread gauge does not sit in the thread properly, very close but not quite right. I'm thinking it may be 0.75mm pitch, my metric thread gauge doesn't have that pitch so can't check.

John

[Michael GilliganParticipant @michaelgilligan61133]

^^^

But I’m very happy to be proved wrong

… any chance of a close-up photo for the benefit of we who are guessing ?

MichaelG.

[John MCParticipant @johnmc39344]

Posted by Michael Gilligan on 01/05/2020 18:55:41:

^^^

But I’m very happy to be proved wrong

… any chance of a close-up photo for the benefit of we who are guessing ?

MichaelG.

Had a go but photos show nothing. Needs a proper studio setup. (Or someone good with a camera!). The thread gauges I have do not fit snug into the cut thread as they do with a known thread. As I said before, close, but not quite.

John

[Michael GilliganParticipant @michaelgilligan61133]

Thanks anyway, John

MichaelG.

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