Use the straight side of this strip ruler to cut 3 1/2" strips. Turn-a-Round the ruler to cut the convex and concave pieces from these 3 1/2" strips. Sew these units together to create 3" finished Corner to Corner Curved units. The holes in the ruler enable the rotary cutter to cut the triangles without damaging the ruler. Use a 28 mm rotary cutter. Our exclusive embedded gripper dots hold the fabric while cutting when pressure is applied.