I'm not sure but I know that to make a HST you add 7/8th to the fabric to come out to the size you want. So if you wanted a 5in finished you'd make the blocks 5 7/8th to get 5. Me, I'd round it up to 6 to make sure it would come out right.

I'd love to see you come back and let us all know which technique works best for you.

HRT are notoriously more tricky than you'd expect, and while I've used pretty much every one of the methods mentioned above, my biggest challenge lies in being able to get absolutely consistent results when piecing many HRT blocks that need to match points.

My favorite method / tool is the tri-rec ruler. You can find youtube tutorials to walk you through the use of the ruler.

If you want to cut rectangles diagonally for the side triangles of a triangle in a square -

You need to cut them 1-1/4 inch longer and a "scant" 3/4 inch wider

Example:

If the finished base size of the triangle is two inches and the finished height size is four inches:

Cut the rectangle 2-3/4 x 5-1/4 inches.

The center triangle:

Add approximately 7/8 inches to the width and approximately 7/8 to the height.

Example: Four inch "finished" base size and four inch "finished" height size:

Cut a strip 4-7/8 wide and the base will be 4-7/8 wide.

P.S. Both triangles cut from a rectangle will go the same direction.

One needs to cut the another rectangle the other direction to get the opposite side of the large triangle.

I lost my tute on these when my hard drive died recently, but this is made different to HSTs. I suggest experimenting with the sizes, possibly cutting 1/2" larger and trim down to size. You place one triangle on top with opposite corners facing, and stitch either side of the centre line.
[ATTACH=CONFIG]519927[/ATTACH]

Gay, that is so true! Can't lay them lined-up right on top of each other. Thanks for the picture. Makes so much sense. I too prefer to make sub-blocks like this and HST over-sized and cut them down to the exact size I need. It takes more time, but makes putting the final blocks together soooo much more accurate and really seems to save time (and headaches) in the end. You gals (and guys) on this board are the BEST!!!!

I think Gay has the right answer. Looks fine to me.

I have a Go die that makes the two color split rectangle.

June Taylor shape cut ruler.