Threads of added strength are produced by twisting plied yarns in the opposite direction to which they have already been twisted, for example, a cord thread with a left twist is made of a number of ply threads with a right twist.

• 加固线是把已经捻过的纱线合股朝相反方向加捻。例如：一般朝左捻的粗线是由数股朝右捻的线合纺而成。