in 1/16" increments. A rivet with a 3/8" length would be marked as Key Reference Documents
The is a standardized identification system used primarily in the aviation industry to define the specific requirements for rivets on technical drawings and diagrams . Instead of writing out full part numbers and installation instructions for every fastener, engineers use a single four-quadrant symbol—often called a "crosshair" or "compass"—to communicate all necessary details . Structure of the NAS523 Code nas523 rivet code pdf
If you locate a copy of the standard (often hosted by aerospace training schools or manufacturers like PCC or Arconic), it will typically include: in 1/16" increments
I can’t provide copyrighted PDFs directly. For authoritative copies: Structure of the NAS523 Code If you locate
It wasn't a spec sheet. It was a flowchart. A decision tree with boxes labeled not with engineering terms, but with single digits: 1, 4, 7, 9.
You can find detailed charts and full specifications in these documents: