From: Wdcockey@aol.com
Date: Wed, 20 Dec 1995 22:12:17 -0500
To: Land-Rover-Owner@uk.stratus.com
Subject: Re: Whitworth - Info.
BA is short for British Association according to my father-in-laws 50 yr old
engineering manual.
BA threads:
BA Bolt diam. Pitch Head
6 2.8mm 0.110in 0.53mm 0.020in 0.193in
4 3.6mm 0.142in 0.66mm 0.026in 0.248in
2 4.7mm 0.185in 0.81mm 0.031in 0.324in
0 6.0mm 0.236in 1.00mm 0.039in 0.412in
Head size is hex across flats and round head diameter
Above from B.S. 93:1919 and B.S. 57:1920
Note that for the bolt diameter and thread pitch the primary dimension is
metric. And that was 75 years ago.
BS and Whitworth hex sizes
BS Whitworth Hex AF
3/16 1/8 .340
1/4 3/16 .445
5/16 1/4 .525
3/8 5/16 .600
7/16 3/8 .710
1/2 7/16 .820
9/16 1/2 .920
5/8 9/16 1.010
11/16 5/8 1.100
3/4 11/16 1.200
7/8 3/4 1.300
I cant see any logical progression of head sizes but Im sure it made sense to
Mr. Whitworth. I believe that the threads are very different from the more usual
Unified & SAE, with different thread pitches. The Series One Club offers a
Whitworth rethreading tool for straightening bolt threads.
RN & AB among others carry Whitworth/BS tools
Snap-On also has Whitworth sockets, but not wrenches
Hope the above is of help.
David Cockey
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