How to sew a mitred corner: Overlock/serge your hem edge, vertical seam edge and the diagonal edge that will become your mitred corner. With right sides facing, fold the angled edge, matching the hem and vertical seam. Sew the angled edges together using a 1cm (3/8”) seam allowance. Turn out and finger press the mitred seam open. Press your mitred corner flat! | Style Arc sewing patterns