User:KDS4444/Silk machine twist

Silk machine twist sizes are another fixed weight system, but the sizes are given as letters rather than numbers, ranging from 000 through A through F and then to FFF. Exactly what length a given letter means was always somewhat arbitrary, based on the manufacturer of the thread, but there is reasonably good agreement on the common sizes A, B and F. Very roughly, size A is 900 yards per pound of thread, and every 100 yards difference is one letter size different. This system is applied to the entire thread, not individual plies. Today this system is found mostly in hand tailoring (where it applies to nylon and silamide threads as often as actual silk). Size A is a general-purpose thread, size B is for heavy seams, and size F is for worked buttonholes.

There is another letter-based thread size system used in US government contracts. Its sizes are very roughly the same as the silk machine twist system, which makes it easy to confuse the two. In this system, size 00 is about T-16, size A is about T-24, size AA is about T-30, size B is about T-45, size E is about T-70, and size F is about T-90. These sizes are controlled by formal specification, not the whims of thread makers; unfortunately, I don't have a reference to the actual spec.

Tire, YLI and other contemporary silk thread makers use a numeric, fixed weight system that I have not pinned down. A size 100 silk thread is very fine, similar to T-10, while a size 15 silk thread is roughly T-40. If anyone knows the length unit for this 1 kilogram fixed weight silk system, I'd appreciate the information.

That by no means exhausts all the thread sizing systems still in use, but it's exhausted me. So let's boil all that down into a table comparing the systems just described. It's worth repeating that the cotton count, Tex, metric ticket, and perhaps denier, systems are the principal ones you will see, unless you are in a specialty area.