The Magnetic Seam Guide attaches to the metal throat plate on a sewing machine. Ideal for ensuring uniform seam width and as a guide to straight stitching. Anti skid design prevents magnet from sliding around while the lightweight, rust-free construction is a step up compared to a traditional metal body. The 3 designs: sewing machine, zipper and tape measure, are presented on a countertop magnetic display board measuring 31 x 22 x 1 (12 1/4″ x 8 1/2″ x 1/2″) and 680g (1.5 lbs). Not recommended for computerized sewing machines.