Mine is 8" long and had rounded edges. It is the only one I have direct experience with. I imagine the different shapes will create a different sound as they pass through the air. You are supposed to give them a light axial spin before swinging the actual string.The twisting of the rope will make it progressively shorter until it again unwinds, increasing the pitch of the note. In open country they can be heard for extremely long distances. Like the whistle, the sound really stands out in the natural world.