[Healeys] Whitworth vs UNC

ahbn6 at verizon.net ahbn6 at verizon.net
Wed Dec 23 09:48:18 MST 2020

There are several articles on bolts on my site on the Technical page Miscellaneous Section


John Sims

 <http://www.healey6.com/> www.healey6.com

Matawan, NJ


From: Healeys <healeys-bounces at autox.team.net> On Behalf Of Curtis Arndt
Sent: Wednesday, December 23, 2020 10:54 AM
To: Roger Grace <roggrace at telus.net>; Healey List <healeys at autox.team.net>
Subject: Re: [Healeys] Whitworth vs UNC


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.






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.



Roger Grace



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