Actually it isn't a tool but I love my Moleskin that I put on my featherweight to make even seams. I cut a piece off the larger piece(Usually about 1/2 inch) measure a slight 1/4 inch from the needle, peel the backing and stick it on the machine. I can zip right along on straight stitching. I change it when my seams look a little off. I have feet that are supposed to have the 1/4 inch but darned if one piece or the other doesn't slide under it. Have those that came with the machines and they aren't any better but I have friends that use them all the time. A useless thing was a piece of plastic that held two pencils so you could add 1/4 inch to an applique piece. Another thing a friend loves.