A frog is a small peice of fabric that you run through your maching when you have finished a seam, but before you detach the seam from the maching. When you do this, you don't have to pull your thread out so far. I used one because it saves yards of thread over a year. I also use it beause when I was taught to sew I was told that you always leave your pressure foot in the down position and it should never be metal on metal, but should be cusioned with a small piece of fabric. I'm not sure if they teach it that way any more. After all, I was taught in the very early 60's and according to my kids, that was at least 150 years ago. Or as one of my sons said, it was rite around the time that they invented the wheel :twisted: :twisted: