HST=Half Square Triangle + the block made by sewing together two triangles. An easy way to make them if you need more than one of a color is to cut two squares from contrasting fabric 5/8" to 7/8" bigger than the desired square. Mark a diagonal line across the two stacked squares, sew a scant 1/4 on each side of the line, cut on the line. Open, press, trim slightly if needed and you have 2 blocks made of contrasting triangles.