This nifty little tool comes in a set of 2 round metal discs. These are used to mark a 1/4" seam allowance with a pen or pencil in the center hole and roll against an acrylic template to easily mark 1/4" away from the template. Great for EPP or to mark free motion quilting lines using a ruler.
To use, simply insert a standard ball-point pen or pencil into the center hole. Then allow the outer edge of the disc to follow the outline of the pattern piece or template.