The Omnigrid quarter square triangle ruler is used to create quarter-square triangles for finished quilt blocks. They are great for cutting half-square and quarter-square triangles. The seam allowances are included in the measurements, which are based on the finished size of the quilt block.Details:Clear8"Includes seam allowances in measurementsEdge markings for accurate measuringDouble-sight lines show up on dark or light fabricLeft- and right-hand numbering and angle systemAcrylicFor use with rotary cutter or straight-edge blade