The Omnigrid 8" half square triangle ruler is used to create half-square triangles for finished quilt blocks up to 8" in size. It has seam allowance calculations included in the measurements; it is easy to manipulate for smaller triangles when quilting. It is used to cut half-square and quarter-square triangles; seam allowances are included in the measurements, which are based on the finished size of the quilt block. You can use it with a rotary cutter or a straight-edge blade. The edge markings allow for accurate measuring and laser cut edges for smooth, deep cutting. The patented double-sight lines show up on light and dark fabrics. It is made from heavy-duty durable acrylic material with left- and right-hand numbering and angle system.Details:8" x 8" x 8"Laser cut edgesDouble-sight linesAcrylic