Three-triangle units are composed of a half-square triangle and two quarter-square triangles - thus 'three-triangle units'.

The half-square triangle element is cut from a square seven eighths of an inch bigger than the finished size of the unit and the quarter-square triangles from ones that are 1¼ inches bigger.

The quarter-square triangle units can be quick-pieced by making HST units from the two QSt squares, marking the diagonal on the HST square, placing it right sides together with the HST squares (make sure the diagonal seam and the diagonal drawn line are at right-angles to each other) and stitching both sides of the drawn diagonal before cutting apart. This will give you two units that are mirror images of each other. Usually however you want ones that are identical.

Start in the usual way - cut two squares for your QSTs 1¼ inches larger than the finished size of the unit (i.e for a 3 inch unit cut 4¼ inch squares).

Mark the diagonals on the lighter square. Mark the stitching lines. If you want the bit triangle on the left and light fabric at the top, mark the seam lines on the left hand side (from the centre) of each diagonal. If you want the mirror image then mark the seam lines on the right hand side. The example shown was marked on the left.

Stitch each seam line - either from the edge to the centre, or the centre to the edge - whichever you find easiest.

Cut apart on both diagonals.

You should have four identical QSTs.

Take the HST squares and cut them in half diagonally - no 'quick-piecing' for this step.

Pair the resulting triangles with the QSTs you just made and stitch.

Press seams to the larger triangles to complete.