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On my Concentrics, I would like to know whether the hexagons are for B.A. or A/F size spanner?

Presuming the adjusters on new cables are the to the same spec. as the originals?

I'm sure mine aren't metric due to the poor fit.


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I think my spanner that fits is a 6 mm that I filed out a bit bigger.


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I suspect they are A/F but I havent (yet) got the small sizes.


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AMAL persisted with British Fasteners and fittings.
I'm not sure what spanners are correct, but a 7mm fits the adjuster, a 9mm is a loose fit on the locking nut.


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IME the adjusters are 2BA. The locknuts are 3BA. I think those are the only 3BA fittings I've encountered.


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On Commando Concentrics, circa 1974, an 11/32 AF spanner fits the locknuts.

Dunno about the adjusters though.
A 2 BA spanner doesn't fit either of them.

11/32 AF equals a 1/8" Whitworth size, so are they plain ole Whitworth/BS ??
I'm not sure what size in Whitworth is smaller than 1/8 , and not sure I have that ?


P.S. CBS claim that the thread for the choke adjuster is 2BA - they sell a plug to blank it off as required.
https://cdn.shopify.com/s/files/1/0717/0717/files/cap-with-plug_large.JPG
Note that the throttle cable hole isn't threaded either - so maybe this all new stuff is different ?

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Perhaps the answer lies in the official AMAL service tools.

The sidefloat version (I think) top has fittings that fit - arrowed.
Sizes not marked.

[Linked Image from i.postimg.cc]

But maybe this is a Concentric tool ??
Both of these are replicas - I've never seen genuine ones ?

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Originally Posted by Rohan
Note that the throttle cable hole isn't threaded either - so maybe this all new stuff is different ?
I thought the throttle cable hole was threaded on those made for BSA. Triumph put the adjustment into the cables and used a top hat. I have examples of both types of carburetor tops.


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Originally Posted by Rohan
On Commando Concentrics, circa 1974, an 11/32 AF spanner fits the locknuts.

Dunno about the adjusters though.
A 2 BA spanner doesn't fit either of them.

11/32 AF equals a 1/8" Whitworth size, so are they plain ole Whitworth/BS ??
I'm not sure what size in Whitworth is smaller than 1/8 , and not sure I have that ?


P.S. CBS claim that the thread for the choke adjuster is 2BA - they sell a plug to blank it off as required.
https://cdn.shopify.com/s/files/1/0717/0717/files/cap-with-plug_large.JPG
Note that the throttle cable hole isn't threaded either - so maybe this all new stuff is different ?

The hex size is 3BA ( the thread is not) the thread for these carb tops are 40tpi ME thread (model engineers) 2BA is something like 31.5tpi (3/16 UNF is 32tpi)


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Originally Posted by DavidP
Originally Posted by Rohan
Note that the throttle cable hole isn't threaded either - so maybe this all new stuff is different ?
I thought the throttle cable hole was threaded on those made for BSA. Triumph put the adjustment into the cables and used a top hat. I have examples of both types of carburetor tops.

Depends which model it’s going on. I believe thunderbolts all had ferule
Tops though Lightnings had adjuster tops. I’m finding that ferule tops
Are much better on Lightnings.


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I should have added that my adjusters are for a '68 twin A65 with Wassell Concentrics.


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Originally Posted by Allan G
The hex size is 3BA

That hex size is for which of them though ?
The Commando Concentrics I have are 2 different hex sizes on the adjusters/locknuts on the carb top.

2BA doesn't fit either of them.
1/8" Whitworth is a good fit on the (larger) locknut.

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I've made an attempt at measuring in situ the hexagons with micrometer and it appears the locknut is 0.315" and adjuster is 0.275".

Just found a 5/16" A/F in some old spanners and it fits perfectly on the locknut.

A 9/32" might be the size for the adjuster, on mine anyway, or the 3 BA mentioned earlier (according to the excellent chart kommando).

Last edited by semprini; 10/03/21 4:46 pm.

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Originally Posted by Rohan
Originally Posted by Allan G
The hex size is 3BA

That hex size is for which of them though ?
The Commando Concentrics I have are 2 different hex sizes on the adjusters/locknuts on the carb top.

2BA doesn't fit either of them.
1/8" Whitworth is a good fit on the (larger) locknut.
Apologies I should have specified. I use 2BA and 3BA spanner’s with accordance to the below quote (though the other way round) the locknuts are larger and thus with BA sizes the smaller the BA number the bigger the hex (or Across flat size) 1ba is bigger than 5ba for example.

From memory I cannot remember how exacting the fit is, a Whitworth size might be a better fit. But your not applying a lot of tension to the adjuster when you tighten the nut. If you apply Enough to round the hex with a 3BA spanner then you’ve probably also damaged the carb top threads in the process. A brush dab of paint on the threads is enough to lock the adjusters so they don’t loosen.

Originally Posted by 2ndchildhood
IME the adjusters are 2BA. The locknuts are 3BA. I think those are the only 3BA fittings I've encountered.


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Just to repeat, I have a 2BA spanner.
It doesn't fit either of them.
Its too large for the small adjuster hex, and too small for the locknut hex.

1/8" W fits the locknut.
Have a set of magnetos spanners someplace ...

I use this hex size chart.
https://www.samstagsales.com/whitworth_table.htm#table

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When I purchased my first tool kit from Sears way back in 1972, it came with a set of what in those days were referred to as "ignition wrenches", three to four inch-long combination wrenches in /32" sizes from 7/32" to 7/16". With these wrenches, and a 6mm and 7mm, I've been able to fit any small nut that I've come across anywhere. I've had Mikunis for a long time now, but I seem to recall using the 9/32" and 11/32" wrenches on the AMAL adjusters.


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11/32" AF is the direct equivalent to 1/8" Whitworth.*
The locknut size on the tops of Commando Concentric throttle and choke cables, it would seem.

I bought a long and strong 11/32" version to do the 1/8"W tappet block nuts on prewar/just postwar Enfields.
Fits them perfectly. Long enough to be able to snug them up comfortably.
https://i.ebayimg.com/images/g/Ca4AAOSw0G1gDVfn/s-l1600.png

*(Actually they'd be a BS/cycle thread size, but I haven't quite come to terms with what those may be called.)
(1/8"W wrenches have become quite difficult to source, at least hereabouts)(and even smaller sizes).

I've seen it writ that anything that is xyz/32" sized in AF is a direct replacement for the hex sizes in the
Whitworth/Cycle Thread world. I think that means that xyz will only ever be odd numbers.

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I guess that means I should buy the 9/32 version for the adjustment hex on the throttle cable ...
Nice and long, so they'll easily go under the tank.
Since I don't seem to have anything this size.*

https://i.ebayimg.com/images/g/AdwAAOSwAkpgCmEi/s-l1600.png

* unless you count the genuine Lucas adjustable wrenchs...
https://thumbs.worthpoint.com/zoom/...360_d8f6c4e32b936e332c29178da7711091.jpg

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It's advantageous that both spanners have minimal "backlash" when tightening/undoing locknut, particularly when adjusting for accurate balance on the vac gauges.


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I'm starting to come around to that maybe they are 2 BA and 3 BA
As they likely should be.

I found a little ex-military 2 BA spanner, and it seems a reasonable fit on the locknut.
Although not perfect - maybe the plating wasn't as thick as intended !
(the other end is 4BA, so no help)

The best fit still seems to be the AMAL all purpose spanner
Although not really a precision tool at all.
I'll see if I can lighten up this pic

https://i.postimg.cc/sXC8s1fJ/Amal.png

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Ha !
Somewhere about here is the realization that the adjuster and locknut sizes on older amals
are different to those on Commando throttle cables.

The older ones could well be 2BA and 3BA.
Not so on a Commando ?
Hmmm.

Wonder where this would all be in print someplace ?

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John Bedford tools (I worked there in the 70s) used to make very nice miniature spanners. The smaller ones are 1/8"AF and 10BA.

[Linked Image from i.imgur.com]


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1/8" AF is a bit different to 1/8" W

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Yes it is, the Whitworth much bigger. I posted the photo just as a matter of interest.


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