DIN 439 LH Low Hex Nut 04. Zn left-hand thread

Steel material. Property class 04. Metric thread, left-hand thread (LH). Bright zinc plated (Zn), moderate weather resistance.

Special nuts are generally considered to be nuts whose design, use, dimensions, or other characteristics differ from 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 welding nuts.
Materials include uncoated or zinc-plated steel (bright zinc, Zn, zinc), stainless steel (A2), and acid-resistant stainless steel (A4).
How to choose the right nut? The rule is that the nut’s hardness, material, and coating should be at least equivalent to those of the fastener used (bolt, screw).