BasicGrey Magnetic Precision Mat Set The 15 by 15 self healing mat is accompanied by an 18 magnetic stainless steel beveled ruler and eight super-strong magnetic tacks. The mat has a perimeter that is marked every 1/8 and an interior marked every 1/2-both with an easy to see white true-sized grid Magnetic attraction makes trimming easy and precise while you e by explore unlimited design options before making a project permanent Metal core inside allows the magnetic tacks to hold down Magnetic ruler to stay in place for practically error-free trimming