Bloc Loc's Half-Square Triangle ruler 1 1/2″ x 1 1/2″ locks onto the seams for instant ruler placement, control so that the seams end 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.