A half-square triangle (HST) is a square made of two triangles, one of each fabric, split on the diagonal. Pinwheels, stars, broken dishes and most of the blocks in the block database are built from them.
Cutting size
Cut two squares 7/8 in larger than the finished size of the unit. For a 2 in finished HST, cut 2-7/8 in squares. Each pair of squares makes two HST units.
Many quilters cut a full inch larger instead (3 in for a 2 in finished unit) and trim the units down after sewing. It uses slightly more fabric and adds a trimming step but every unit comes out exact. The patterns here use the 7/8 in rule for yardage, so cutting at a full inch is still covered by the allowance.
Steps
- Place the two squares right sides together, the lighter one on top.
- Draw a line corner to corner on the light square.
- Sew a 1/4 in seam on each side of the line.
- Cut on the drawn line. You have two triangles-of-two.
- Press each open, seam toward the darker fabric.
- Trim to the unfinished size (finished size plus 1/2 in), keeping the diagonal seam running exactly corner to corner.
Which way does it point?
In the pattern's block diagrams, "A/B" means the diagonal runs from bottom-left to top-right with fabric A in the upper-left half; "A|B" runs the other way with A in the upper-right. The rendered layout shows every unit turned the right way, so when a block is rotated in the layout you can follow the picture rather than re-reading the token.
Batch counts
The cutting table in a pattern says, for example, "15 HST squares (pair with W, makes 30)". That is 15 squares of this fabric paired with 15 squares of fabric W, producing 30 units.