Heavy Hex Nuts are washer faced, are slightly larger and thicker than standard hex nuts. The heavy hex nuts is typically used for large diameter 10.9 grade high strength bolts which makes them the strongest of comparably-graded nuts. Their additional strength comes from increased thread engagement, which is due to their thickness, and greater resistance to dilation (expansion or stretching) because of their larger width. The heavy hex nut's increased size yields a larger bearing surface and improved wrench ability. "Hex" is for hexagon, which means they have six sides. They are also known as: heavy nuts or steel structure nuts.