Re: Unbreako - R, S, or T

In a message dated 2/3/01 9:55:50 PM Pacific Standard Time, 
cfchrist@earthlink.net writes:

<< most of the standard hardware on my bugeye
 carries the "R" marking on the head of the bolt with a depressed circle in
 the center of the head of the bolt.  >>

Hi Charles

The only reason for the depressed circle is the British way to differentiate 
a UNF threaded fastener from a BSF/BSW (Whitworth form) threaded fastener.  
This came about during the mid 50's when the U.K. standardized from Whitworth 
to the Unified Thread Form which is equivalent to SAE.

Curt Arndt
Carlsbad, CA
'55 BN1, '60 AN5