Half-Square Triangle The half-square triangle (HST) is one of the most useful units that can be included in a block or a quilt. This is my absolute favorite unit as it can be used in so many different ways to accent a design. There are many, many ways to create HSTs...the way that I'm going to explain here is my prefered way of creating the unit. This is not to say it is the best way, only the way that I use to get consistant sized units. We will be making 4 HSTs to create a 6" finished block. The rule for cutting squares for HSTs is to add 3/8" to the unfinished size of a square for the same area. For example...the unit needs to fit a 3" space, so you would cut 3-1/2" + 3/8" = 3-7/8" square. I can't create these units the same size to save my life, so I add an additional 1/8" to be sure I don't get them too small...and to make cutting easier.