This is a special machine stitch that looks like a combination of straight and zigzag stitches. It’s sewn close to or over the raw edge of the seam allowance.
Effective at keeping the raw edges of a seam allowance from fraying. Adds little bulk to the seam allowance.
You must have a sewing machine capable of making this stitch. Doesn’t look as neat and clean as some other methods.
How to Make
Trim the raw edge of the seam allowance (to make a clean edge). Set your machine to the proper stitch design (consult your manual). Stitch so that the point of the overcast stitch falls at or just beyond the raw edge of the seam allowance.
You can either press the seam allowance open and overcast each edge separately or leave the seam allowances together, overcast them together, and press the seam allowance to one side.