Gran was born in 1857 and died in 1956. I recently received her crochet hooks from my father when he was cleaning things out. She had sizes 6 1/2 – 1. (Note: I don’t know the accuracy of this site, it appears to be from the US and Gran’s needles are from the UK but it gives you an idea of how small they are.
The thread in the corner of the photo below is Kid Silk Haze.