I have that die, have not used it yet and am not in my sewing cave but.........I am guessing a HST with the bias edge against the hex is what you need....so measure one of the edges of the hex and that would be the long line of your triangle (forgot the "official" name of that line) long time since math class!!!!!or just lay cut hex on paper and with ruler extend one of thlines in two direction for FINISHED SIZE of HST--remember hex does NOT have 1/4"seam allowances on die....it is the finished hex..........if you use the cut edge as 1/4" allowance then refigure your HST.........I think on Accucut website there is a chart somewhere that will give you what you need faster than this......