Hex nuts and bolts join parts together and are mated in size (metric or standard), hole diameter and thread pitch as well as width and thickness. The hex nut corner angles prevent rounding off during the tightening process.
Hex nut sizes available in most American hardware stores include standard sizes, ranging from 8 and 10 (less than 1/4 inch) to fractions of an inch (from 1/4 inch to 3 inches), indicating their thread hole diameters. Hex nut thread holes must match the hex bolt post diameter and thread pitch in order to tighten properly.
Width Across Flats
Hex nut measurements from one flat edge to the opposite flat edge range from an average 11/32 inch (size 8) to 4.5 inches (size 3), with slight variations depending on manufacturer, material (brass, steel) and oxidation-preventive coating.
Width Across Corners
Hex nuts range from a minimum 3/8 inch (size 8) to maximum 4.959 inch (size 3) when measured from one of the six corners to the opposite corner.
Standard Hex Nut Thickness
Standard hex nut thickness runs from a minimum 3/16 inch (size 8) to a maximum 2.654 inches (size 3).
Hex Jam Nut Thickness
Hex jam nuts, used to tighten against standard hex nuts and lock them in place, run from an average 5/32 inch (size 1/4) to an average 1 19/32 inch (size 3) in thickness.