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Re: British or SAEt

To: "Paul Dorsey" <dorpaul@negia.net>,
Subject: Re: British or SAEt
From: "Michael Marr" <mmarr@notwires.com>
Date: Tue, 12 Apr 2005 22:35:37 -0500
There are a couple of major differences.  First, the included angle of the 
thread is 60 degrees on American threads and 55 1/2 degrees on the British 
Standard Whitworth (BSW) and British Standard Fine (BSF) threads.  Second, 
there are indeed differences in pitch.  For example, a 1/2 in UNC bolt has 
13 tpi, whereas a 1/2 in BSW bolt has 12 tpi..  A 5/8 bolt has the same tpi 
in both standards, but the difference in thread form would make a nut and 
bolt of the different standards bind.

The other difference is in the size convention for wrenches, or spanners if 
you're on the UK side of the pond.  A half inch unified wrench fits a bolt 
with a head measuring 1/2" across flats (or AF, which is what these wrenches 
used to be called in England).  A half inch spanner, on the other hand, fits 
a half inch diameter bolt, which has a hex that is between 0.812" and 0.820" 
across flats.

So, there you have it.

Michael Marr
1960 TR3A
Naperville, IL, USA
Ex: Tilbury, Essex, England.


----- Original Message ----- 
From: "Paul Dorsey" <dorpaul@negia.net>
To: "triumph list" <triumphs@autox.team.net>
Sent: Tuesday, April 12, 2005 9:55 PM
Subject: British or SAEt


>I had someone tell me that the British used a different 'pitch' on the 
>thread
> of a bolt.  IOW, a SAE 7/16 x 24 (threads/inch) but, perhaps the closest
> British sized bolt is 7/16 x 25 tpi.  Is this true or is that guy making 
> this
> something that "the British did this on purpose".HWNM (his words not 
> mine).
> Thanks,
> Paul Dorsey
= 




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