DIN 9021 refers to a specific standard established by the Deutsches Institut für Normung (DIN), which outlines the dimensions and specifications for flat washers. These washers are typically used in conjunction with bolts and nuts to distribute the load of the fastener, thereby preventing damage to the surface being fastened and ensuring a secure connection. The standard provides detailed information regarding the material composition, thickness, and diameter of the washers, which are essential for ensuring compatibility and performance in various mechanical applications. Adhering to DIN 9021 is crucial for manufacturers and engineers to maintain quality and reliability in their fastening solutions.