Omnigrid Ruler Right Triangle 45 Degree Up To 6" Square- used to create half-square triangles for finished quilt blocks up to 6in; it has seam allowance calculations included in the measurements; it is easy to manipulate for smaller triangles when quilting. 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.