British nut/bolt sizes

[ian@Centric.COM (Ian Macky)]

I found the following useful table in the BTC catalogue:


    S O C K E T S   &   W R E N C H E S   ( S P A N N E R S )

                      Key to Nut & Bolt Sizes

      nut size across flats                   British sizes
  -----------------------------           --------------------
  decimal inch    mm    AF inch           BA      BSF      BSW
      .250         .      1/4      .       .       .        .
      .276         7       .       .       .       .        .
      .282         .       .       .       3       .        .
      .313         .      5/16     .       .       .        .
      .315         8       .       .       .       .        .
      .324         .       .       .       2       .        .
      .340         .       .       .       .      3/16     1/8
      .344         .     11/32     .       .       .        .
      .354         9       .       .       .       .        .
      .365         .       .       .       1       .        .
      .375         .      3/8      .       .       .        .
      .394        10       .       .       .       .        .
      .412         .       .       .       0       .        .
      .433        11       .       .       .       .        .
      .438         .      7/16     .       .       .        .
      .445         .       .       .       .      1/4      3/16
      .472        12       .       .       .       .        .
      .500         .      1/2      .       .       .        .
      .512        13       .       .       .       .        .
      .525         .       .       .       .      5/16     1/4
      .551        14       .       .       .       .        .
      .563         .      9/16     .       .       .        .
      .591        15       .       .       .       .        .
      .600         .       .       .       .      3/8      5/16
      .625         .      5/8      .       .       .        .
      .630        16       .       .       .       .        .
      .669        17       .       .       .       .        .
      .688         .     11/16     .       .       .        .
      .709        18       .       .       .       .        .
      .710         .       .       .       .      7/16     3/8
      .748        19       .       .       .       .        .
      .750         .      3/4      .       .       .        .
      .787        20       .       .       .       .        .
      .813         .     13/16     .       .       .        .
      .820         .       .       .       .      1/2      7/16
      .866        22       .       .       .       .        .
      .875         .      7/8      .       .       .        .
      .920         .       .       .       .      9/16     1/2
      .938         .     15/16     .       .       .        .
      .945        24       .       .       .       .        .
     1.000         .       1       .       .       .        .


Would someone explain the British side of this table, *please*??
BSW 1/2 = BSF 9/16 = .920"??  Ahalfa WHAT?  How big is a FULL BSW?

I corrected a number of the mm- and AF-dec.in. conversions which were
truncated, not rounded (which makes me worry about the British values
too) and filled out the big end of the table some.

Note the reverse BA numbering, where the the smaller the number the
larger the size...!  Eh?

--ian