Quilting Dictionary Quarter-Square Triangle (QST)PiecingShare this Facebook Pinterest X WhatsApp Email Copy linkA pieced unit made from four triangles sewn together, used when you need the straight fabric grain running along all four outer edges of a square. Half-Square Triangle (HST) Quarter-Square Triangle (QST) Half-Rectangle Triangle (HRT) Quarter-Square Triangle (QST) Geometry Four quarter triangles meeting at a central cross-seam, keeping straight fabric grain along all 4 outer edges.