tn This is the active participle, not the passive. It would normally be rendered “joining together.” The Bible uses the active because it has the result of the sewing in mind, namely, that every curtain accompanies another (U. Cassuto, Exodus, 348).
9
tnHeb “a woman to her sister,” this form of using nouns to express “one to another” is selected because “curtains” is a feminine noun (see GKC448§139.e).