Length is measured under the head (grip length + clinch allowance).
Y = number of 16ths of an inch.
Example: Y=8 → 8/16" = 1/2" length.
For flush riveting, the PDF includes the exact radius and depth of the 100° countersink. A mismatch between the rivet head and the countersink angle creates a stress riser. The NAS523 PDF includes go/no-go gauge dimensions. 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: Length is measured under the head (grip length
Disclaimer: Aerospace standards (NAS, AN, MS) are copyrighted specifications controlled by standards organizations (like AIA/SAE). While you can find "guides" based on these standards, the official PDFs usually require a license to access legally. Disclaimer: Aerospace standards (NAS
NAS stands for National Aerospace Standard. NAS523 is the specific standard that dictates the "Code for Rivets and Their Installation."
Before NAS523, different manufacturers might have used different codes to identify similar rivets. This created chaos in the supply chain and on the maintenance hangar floor. NAS523 standardized this into a logical format that tells you everything you need to know about a fastener just by looking at its part number.