This is the Quick Curve Ruler from Sew Kind of Wonderful. The Quick Curve Ruler comes with a free pattern called "Urban Runner". The ruler is to be used with all Sew Kind of Wonderful patterns. It is used to cut the curve shapes out and square the blocks up after piecing. The ruler is a quality acrylic ruler with a curved cut-out where your rotary blade - regular or jumbo - will fit into. It's 7" x 12" in size and has a hang hole for storage convenience.