I always buy the small rippers by the dozen at Atlanta Thread & Supply. They have the little red plastic ball on the short side. When they get dull, just throw them out! Some times it's the technic used to rip. My Mom always cut a thread every few stitches on the top, then turn the fabric over and cut in between the top cuts on the bobbin thread. When I worked in a children's clothing factory, they were amazed how much quicker they could rip this way.