Foot controller Model 21371 is for use with sewing machine Model MC6600P. 7 When stitches D1, D2, 8, 9 Mode 1, D01, D02, 08, 09 Mode 2 and 01, 02 Mode 3 are selected, the machine will immediately sew locking stitches when the Auto-lock button is pressed, then automatically stop. When sewing any other stitches,