Button hole scissors. You set that screw so you don't accidentally cut through the stitching at the end of the place you want to cut open. The pointy things on the blades will make the original hole in the fabric and you cut to the end. I don't recall ever using the tips of the blades to actually cut the buttonhole open. It's a lot more accurate than anything else I've used. That seam ripper can slip and rip through the stitching awfully easy--guess how I know!