SINGER 6550-WORKBOOK Scholastic - Manual (Page 27)

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Attach the Buttonhole Foot to the machine, taking care not to displace
the cord. (See sewing machine instruction manual)
The foot will hold the cord in the correct position as the machine
stitches the buttonhole.
Sew the buttonhole, following the One-Step Buttonhole instructions
in the machine instruction manual.
The zigzag section of the buttonhole will stitch over the cord.
After stitching is completed, pull the excess cord tails tight. This will
pull the cord into the buttonhole.
Cut off the excess cord.