ASME B18.6.3 Plain Brass Machine Screw Hex Nut, #4-40 Thread Size, 3/32" Width Across Flats, 1/4" Thick (Pack of 100)
Most often used on machine screws and threaded rod, these general purpose nuts are for low-strength assemblies.  Hex Nuts have flat tops with chamfered corners; bottoms may be flat or chamfered.  Hex drive systems are driven with a wrench.Brass is rust proof, corrosion resistant and polishes to a rich, golden color.  Brass is easily soldered and brazed and accepts plating readily.  The typical composition is 70% Copper and 30% Zinc.  Strength increases with a higher percentage of Zinc.A threaded fastener's size name includes information about the major external diameter, followed by the threads per inch, which indicates if it is coarse or fine.  Coarse threads are better when working with brittle materials; they are sturdier and are easier to thread and unthread compared to fine.  Coarse threading also allows for thicker coatings and platings.