The Hebrew phrase
appears throughout Exodus, and it usually occurs paired with "Shesh Mashzar", but I suppose someone can know the answer to one question without knowing the answer to the other. This is easier to figure out, because the words imply that it is somehow twined twice.
I had a thought that this means knitted work, since knits are twined once to make the thread, then again to knit the thread into a work that can be finely patterned. The whole thing is made by a "Rokem" which I thought might be best translated as an embroiderer.
I am not sure about this translation choice, but I have a little more confidence about this than about Shesh. Is "knit" a reasonable interepretation "tola'at sheni"?