Someone may have already said this but here is my explanation of how to get the right measurement. If you were to take the center square (on paper) and mark it corner to corner diagonally you will have 4 triangles. If you measure each of these triangles, they are the size needed to put around your square. Don't know if this makes sense but it works for me.

it does have many names - another one is Economy block

Creative Grids has three rulers that make the 5", 6" and 8" square in a square block.

Maybe these drawings may help explain why the squares for the HSTs and QSTs are cut the sizes they are?

(or maybe they will just confuse the issue) - - -

Vicki, I saw this on Missouri Quilt Co. site. They have a tutorial on making and expanding this block. I want to try it.