Sinned, I'm not looking for what thread to use today. I know what is currently available, what works best for me and my reader, and why; I'm interested in the hy of tailoring, techniques, and findings that have been used in the past. Specifically I'm looking for old tech. which have been forgotten.
Silk threads are not always monofilament, Cotton also rots when it's dried out. I see this often on museum garments.
The "thread" described was used for sewing, sold in skeins, size #35. Silk is described separately and "may be obtained in various degrees of fineness." In another paragraph tailors' cottons range from "stout no. 24 to fine 40 on reels".
"...for strong seams, thread, not cotton, must be substituted for silk."
The quotes are directly from the book which is part of the "Work" handbook series. The book has very few diagrams, but the directions are good.
Fronno, it's possible that this is just a lightweight thread without a twist. I'll continue reading to see how it's used.