Half-Square Triangle Ruler Set #2Bloc Locs Half Square Triangle Set #2 contains 2 1 2, 4 1 2 and 6 1 2" rulers that lock onto the seam for instant ruler placement, control so that the seam ens 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.