[Healeys] Whitworth vs UNC

[Bob Haskell]

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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