Author Topic: Altette Horn thread size  (Read 372 times)

Offline TimK

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Altette Horn thread size
« on: 18.11. 2019 00:17 »
Hi Everyone

Does anyone know the thread size of the "coil core locking nut" on the rear of the horn?

Cheers
Tim
Tim Kerridge
Australia

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Re: Altette Horn thread size
« Reply #1 on: 18.11. 2019 09:07 »
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Offline Swarfcut

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Re: Altette Horn thread size
« Reply #2 on: 18.11. 2019 16:10 »
Without a horn to hand, my guess is that Old Joe Lucas would use a BA  (British Association) Thread as this is the common thread favoured at the time for electrical  components.

 Thread is a basic 47.5 degrees, for all sizes, Largest size (0 BA) has  Nominal diameter  0.2362", Minor diameter  0.1890" and  25.4 TPI, ( a real oddball system) The TPI changes for every reduction in diameter.  See if your bits are anywhere near to  dimensions on published data tables.

 Smaller sizes in this system are identified by a larger numerical designation, up to 12BA at 0.0512" nominal diameter, with a TPI of 90.9!

 Apologies in advance if I am completely wrong, but it is a good place to start.

   Taff the horn is always worth scanning for a little light relief, but be careful working with horns all day........



Swarfy.

Offline trevinoz

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Re: Altette Horn thread size
« Reply #3 on: 18.11. 2019 20:40 »
That would be 9/16" x 32 t.p.i.
Just one of the many Lucas bastard threads.

Online duTch

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Re: Altette Horn thread size
« Reply #4 on: 18.11. 2019 23:00 »

 
Quote
..........  ...... and  25.4 TPI, ( a real oddball..

 That equates to 1.0mm pitch  *conf2*
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Offline trevinoz

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Re: Altette Horn thread size
« Reply #5 on: 19.11. 2019 21:03 »
B.A. is a metric thread, Dutch.

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Re: Altette Horn thread size
« Reply #6 on: 19.11. 2019 21:19 »

 
Quote
B.A. is a metric thread, Dutch.

 I've long suspected that but never saw it documented.... *conf2*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online groily

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Re: Altette Horn thread size
« Reply #7 on: 20.11. 2019 17:42 »
http://mdmetric.com/tech/thddat8.htm#ba

There you go DuTch - Doesn't say 'It's a Metric Thread Form' in as many words, but you'll see all the major diameters are roundish numbers/fractions in metric, going down in a series of carefully-planned steps from 0BA at 6 x 1mm.
Spanner sizes which don't really overlap a whole lot with fractional AF sizes, but 4BA is 1/4 AF - and that's the commonest one we need.
Bill

Offline Colsbeeza

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Re: Altette Horn thread size
« Reply #8 on: 20.11. 2019 20:31 »
Swarfy,
At my age, it is a while since I had a horn in my hand.
Col
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Offline trevinoz

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Re: Altette Horn thread size
« Reply #9 on: 20.11. 2019 20:45 »
I thought you were one, Col.

Offline TimK

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Re: Altette Horn thread size
« Reply #10 on: 21.11. 2019 03:56 »
Thanks guys, it's definitely a bigger diameter than any of the BA options and looking at the thread I'd say that trevinoz's 9/16 x 32 tpi looks a very good candidate.

Cheers
Tim
Tim Kerridge
Australia

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Re: Altette Horn thread size
« Reply #11 on: 21.11. 2019 09:35 »
http://mdmetric.com/tech/thddat8.htm#ba
but 4BA is 1/4 AF - and that's the commonest one we need.

4BA is considerably smaller than 1/4 AF?

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Re: Altette Horn thread size
« Reply #12 on: 21.11. 2019 09:53 »
Yes - but Across the Flats spanner jaw size Rex, not shank diameter  . . .
Standard  hex on say, UNF or UNC 1/4" screw/bolt, is 7/16" across, which is v close to 3/16" WW - aka 1/4" BSF.

I fully understand why all my mates here where I am are perfectly happy with metric on their 'Continental European' machinery!
Bill

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Re: Altette Horn thread size
« Reply #13 on: 21.11. 2019 11:12 »
I fully understand why all my mates here where I am are perfectly happy with metric on their 'Continental European' machinery!
*lol*
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Re: Altette Horn thread size
« Reply #14 on: 21.11. 2019 14:46 »

 
Quote
........I fully understand why all my mates here where I am are perfectly happy with metric on their 'Continental European' machinery!

 Yes true as- but the actual fasteners are not always available from a regular nut and bolt shop either....Auto/Moto threads are usually ISO fine -or ?- instead of hardware coarse  eg; Moto G frame joint 12mm x 1.0 (?) socket heads  *pull hair out*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia