You will have to make a grid and your squares will have to be 7/8" larger than the finished triangle square. For example: If finished triangle square is 4", make the grids 4 7/8".

In the example below, I wanted 12 triangle squares. Using 2 color fabrics and making a grid on light colored fabric, I made a grid of 6 squares, each 4 7/8" x 4 7/8" as shown by the black lines.

Layer this gridded fabric over your contrasting fabric and stitch according to illustration. A sewing line is designated by the blue lines and the direction by red arrows. The seam is ¼" away from the drawn grid line. After sewing, cut the vertical, horizontal and diagonal pencil lines to separate the triangles. The results are 2 triangle squares from each drawn square for a total of 12 triangle squares.