Fastener diameter and manufacturer head location.
The NAS523 code is a standardized practice that includes all types of fasteners that undergo permanent deformation during installation. Removing these fasteners typically requires their destruction, making precise initial installation essential for structural integrity. nas523 pdf
Often identifies an MS20426AD rivet (countersunk 2117 alloy). ↗️ Northeast (NE): Diameter & Head Placement Fastener diameter and manufacturer head location
Often identifies an MS20470AD rivet (2117 aluminum alloy). nas523 pdf
The system uses a symbolic "cross" located on blueprints to give technicians immediate instructions for a specific location: Part number and material alloy code.