I make a lot of HST from scraps and I love the little quarter inch ruler. Makes marking the sewing line go real fast. There are two lengths to choose from. I have both and love them.
They are 1/2" wide with a mark down the center length of the ruler. Just line this mark up on the diagonal corners of any size block and draw a light line on each side of the ruler. Sew on the lines and cut down the center.
I think they are from Fons and Porter and I love them!
peace