Torcere / Twisting
A silk throwing mill.
From: L'arte della Seta in Firenze. Trattato del secolo XV. (1487)
Doubling and Throwing:
This step is optional. Silk without twist is often used in embroidery and weaving, and has a high luster.
To make a thicker thread, you can take two or more reelings and twist them together (called "doubling") on a spinning wheel.
"Throwing" involves taking two or more of those twisted threads, and twisting them together in the opposite direction.