DIN 439 MF hex nut A2-035 fine thread

Material: A2 stainless steel. Property class A2-035. Metric fine thread (MF). A2 stainless steel with good corrosion resistance.

Special nuts are nuts whose design, application, dimensions, or other properties differ from those of a standard hex nut.
Examples include low nuts (thin nuts), flange nuts, castle nuts, rivet nuts, square nuts, diamond nuts (diamond-shaped profile), sheet metal nuts, and weld nuts.
Materials include uncoated or zinc-plated steel (bright zinc, Zn, zinc), stainless steel (A2), and acid-resistant stainless steel (A4).
Choosing the right nut? The rule is that the nut’s hardness, material, and coating should be at least equal to those of the fastener used (bolt, screw).