This presser foot is used for sewing the straight stitch with the centre needle position.

The guidelines on the right side at the front of the presser foot allow you to check the positions at about 0.1”, 0.2”, 0.3” (3mm, 5mm, or 7mm) from the needle.

Since the needle drops into a small round opening, the seam is stabilized to create a perfect straight stitch.