Altette Horn thread size

[TimK]

Hi Everyone

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

Cheers
Tim

[Sav]

http://taffthehorns.com/

[Swarfcut]

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.

[trevinoz]

That would be 9/16" x 32 t.p.i.
Just one of the many Lucas bastard threads.

[duTch]

 

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

 That equates to 1.0mm pitch 

[trevinoz]

B.A. is a metric thread, Dutch.

[duTch]

 

B.A. is a metric thread, Dutch.

 I've long suspected that but never saw it documented....

[groily]

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.

[Colsbeeza]

Swarfy,
At my age, it is a while since I had a horn in my hand.
Col

[trevinoz]

I thought you were one, Col.

[TimK]

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

[Rex]

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?

[groily]

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!

[morris]

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

[duTch]

 

........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