: Companies like Boeing or Piper may use proprietary variations (e.g., BAC codes) that cross-reference with NAS523 standards .
If you used a standard rivet from the shelf, the wing would hold for 100 hours. If you used the correct coded rivet—7-4—it would hold for 10,000. The "code" was the map. 7 meant "Armstrong alloy, heat-treated to spec T-74." 4 meant "reverse countersink, 100-degree seating."
: Companies like Boeing or Piper may use proprietary variations (e.g., BAC codes) that cross-reference with NAS523 standards .
If you used a standard rivet from the shelf, the wing would hold for 100 hours. If you used the correct coded rivet—7-4—it would hold for 10,000. The "code" was the map. 7 meant "Armstrong alloy, heat-treated to spec T-74." 4 meant "reverse countersink, 100-degree seating." nas523 rivet code pdf