Half-Square Triangle Ruler Set #3Bloc Locs Half Square Triangle Set #3 contains 1 1 2, 3 1 2 & 5 1 2 rulers that lock onto the seam for instant ruler placement, control so that the seam ends in each corner and trims 90% faster than a flat ruler. Ruler rock is gone, too! Also trims quarter square triangles, birds in the air, y blocks, LeMoyne Star, double windmill, hidden square units and much, much more! HST ruler is multi sized and trims in 1 8 increments.