The Omnigrid® 8 inch half square triangle ruler is used to create half-square triangles for finished quilt blocks up to 8"; it has seam allowance calculations included in the measurements; it is easy to manipulate for smaller triangles when quilting. In general, Omnigrid® triangle rulers are 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.