slide fastening chain together at that point an apparatus for manufacturing a plurality of the trouser fly units of fig1 is shown in fig2 and includes a sewing machine 40 a gapper bottom stop applier and cutter 42 and a stacker 44 all mounted on a suitable support such as a table top 46 the sewing machine 40 is a conventional sewing machine except for a modified presser foot 48 as described herein which includes at least two spaced sewing mechanisms one including the needle 45 fig6 and trimmer 77 fig5 for forming the line of overedge stitches 14 and the other including the needles 41 and 43 for forming the lines of straight stitches 18 and 20 alternately the sewing machine 40 can have a stitching mechanism with only one needle for forming a single line of straight stitches in place of the double line of stitches 18 and 20 the gapper bottom stop applier and cutter 42 is a conventional apparatus or assembly of apparatus for forming the gaps 30 and 32 applying the bottom stops 34 and severing the continuous chain 16 between the fly pieces 10 the stacker 44 is a conventional mechanism for forming stacks of the fly units alternately a receptacle or bin may be provided in place of the stacker 44 to receive a plurality of the trouser fly units feed wheels 50 52 and 54 are provided at the output of the sewing machine 40 at the input of the gapper bottom stop applier.