Thanks for your input into this grey area, I say grey, as to me it still remains so. William Westwood's list is that of the exempted items that were listed in the Plate Offences Act of 1738, this part of the Act was never repealed in Victorian times and to my knowledge was current at the time of his letter that was published in Thomas B. Wigley's book. The Act uses the term 'bracelets', something that, again to my knowledge, referred to fairly lightweight chains or thin bands at this period.
This was the closest reference I came across as to how articles of jewellery had changed over the years, taken from a Parliamentary Committee in 1878 when James Garrard was questioned:
Q. You are aware that there are many articles of gold which are not compelled to be hallmarked? Take, for instance, a gold watch chain?
A. At the date of the Act (1738) at which those exemptions were made, the class of chain made was a light chain that would collapse under the punch, and such as could not have been marked. If you have a chain that your grandfather wore, you will see it is a chain unlike those of the present day.
I wonder if exempting the much heavier-weight bangles was ever in the spirit of the Act. It would be interesting to see if any of the other offices adopted the same interpretation of the Act, or was Westwood looking after the interests of the Birmingham jewellery trade?
As a side note, one thing I did learn about bangles (and other hollow work) that I often wondered about, was how the marks were stuck without the article collapsing under the pressure of the punch, apparently the manufacturer would supply the assay office with a correctly sized and shaped tool to insert into the item whilst the marking is taking place, simple.
I guess that was a typo, the date letter 'h' - 1882