The AIA is the copyright holder. For industrial use (AS9100 audits), you need a paid, controlled copy.
The defining feature of a NAS 523 bolt is the flange head. The standard typically specifies two variations of the flange bearing surface: nas523 pdf top
While MIL-STD-105 was canceled in 1995, NAS523 remains active and is enforced by major primes like Boeing, Airbus, Northrop Grumman, and Spirit AeroSystems. The AIA is the copyright holder