This presser foot accomplishes several steps in a single sewing operation.
The scroll on the front of the presser foot turns the fabric edge under twice. The double-turned hem stops the fabric edge from fraying later.
A guide in the presser foot sole guides the turned-under fabric to the needle hole, where the fabric is sewn with a straight stitch into a sturdy 4 mm wide hem. The finished hem then easily advances underneath the foot, enabling smooth sewing.