The object of the invention is to improve the construction and simplify the operation of the class of sewing machine in which a rotary loop taker enters and opens a loop of needle thread and winds it around a and carries it around a bobbin whose only movement is that of the bobbin, whose only movement is that around its own axis or center, and the extent of the latter movement is only that due to the pull of the thread as the thread is consumed to form the stitch.