The rational sewing of assembly seams is the speciality of the double-chainstitch machine 171. It allows especially high sewing speeds. Due to the automatic adaptation of the lower thread supply to the stitch length an always superb stitch formation is guaranteed. The thread trimmer - standard equipment depending on the subclass - and the stitch condensing allow a safe beginning and ending of the seam within the material. Further characteristics are the smoothness of running, even at high speeds, and the simple thread leads.