Vintage hooks and needles
Conversion charts to modern sizes.
Even though the first crochet patterns books started to show up in England and America in the 1840’s (there were magazine articles in Europe before then), manufactured crochet hooks were already available, and several brands of hooks were recommended in the early pattern books.
Each manufacturer had its own sizing system.
Many lace makers, especially in Ireland, made their own hooks from a bent needle with a cork or wood handle.
By 1900 or so, there was a little more size standardization, but even today there are significant differences between manufacturers, even in metrically sized hooks.
Much of this information on this chart came from manufacturers’ listings and my own hook collection. Many inconsistencies were resolved with generous help from members of crochetpartners.org.