[Healeys] Whitworth vs UNC

[Michael Salter]

Thanks Bob  ... I  think you have nailed it.

M

On Wed., Dec. 23, 2020, 12:46 p.m. Bob Haskell, <rchaskell at earthlink.net>
wrote:

> Michael,
>
> I'm going to guess 1/4" BSP.  0.518" OD - 19TPI.
>
> https://britishfasteners.com/threads-bsp
>
> Cheers,
>
> Bob Haskell
> Austin Healey 3000 BN7/BT7 registrar
>
> On 12/23/20 11:30 AM, Michael Salter wrote:
> > Well I have one for you Curt.
> > The thread on the oil drain back pipe on the 100 engine (1B1236) has
> > me stumped.
> > The tube is 0.500" O.D. with an I.D. of 0.362"
> > The OD of the thread is 0.511" and it is 19 T.P.I.
> > I cannot find a 19 TPI x 1/2" pipe or tube spec anywhere .... any ideas?
> >
> > M
> >
> >
> > On Wed, Dec 23, 2020 at 10:54 AM Curtis Arndt <cnaarndt at gmail.com
> > <mailto:cnaarndt at gmail.com>> wrote:
> >
> >     Here is an excerpt from one of my articles...
> >
> >     On Tue, Dec 22, 2020 at 1:48 PM Curtis Arndt <cnaarndt at gmail.com
> >     <mailto:cnaarndt at gmail.com>> wrote:
> >
> >         The bolt is 5/16" BSW!   Don't let anyone tell you different.
> >
> >         Even my 45K original mile '60 Bugeye has its original 5/16"
> >         BSW bolt in the generator front plate.  The problem arises
> >         since a 5/16" UNC bolt has the same tpi (threads per inch) as
> >         the 5/16" BSW bolt.  The issue is that UNC has a thread pitch
> >         angle of 60° and Whitworth by definition is 55°. The wrong
> >         bolt will never torque properly and will eventually wear the
> >         aluminum generator front plate.
> >
> >         Cheers,
> >
> >         Curt
> >
> >         On Mon, Dec 21, 2020 at 3:53 PM Roger Grace
> >         <roggrace at telus.net <mailto:roggrace at telus.net>> wrote:
> >
> >             My understanding is that they are close but not
> >             interchangeable ?
> >             Thread angles are slightly different.
> >
> >             For AH generator adjusting link is this 5/16 W or 5/16 UNC ?
> >
> >             At back of my mind think they should be Whitworth -  think
> >             you told me that is why they come loose if you use UNC ?
> >
> >             Finding it difficult to identify one from the other.
> >             Any tips to do this welcome.
> >             Have a definite W bolt and comparing to UNC can only see
> >             slight rounding of UNC ?
> >
> >             Moss sent me a UNC bolt for this link - well that is what
> >             they called it ?
> >
> >             Would appreciate your expert input.
> >
> >             Regards,
> >             Roger Grace
> >
> >
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