Here are the key historical revisions you need to know about:

3. Southwest Quadrant (SW): Sheet Metal Preparation (Dimpling vs. Countersinking)

2117 aluminum alloy (AD rivet, most common for structural repairs). Raised Dot: 2017 aluminum alloy (D rivet).

The NAS523 symbol system organizes critical fastener data into four quadrants (NW, NE, SW, SE) centered on a cross. NW (Northwest - Upper Left):

Provides details for dimpling or countersinking. This section instructs the technician on exactly what type of prep work is required for the installation.

If you are a student or non-commercial user, check public libraries with "Aerospace Standards Access" or university engineering portals that subscribe to SAE Mobilus.

: Dimpled hole preparation (used on skins too thin for machine countersinking).

The core of the NAS523 document is the four-quadrant symbol. Each corner holds specific information that tells a technician exactly which rivet to use and how to install it. 1. Northwest (NW) Quadrant: Part Number & Material

Because NAS523 is a proprietary industry standard maintained by the Aerospace Industries Association (AIA), the complete, official text is typically behind a paywall on technical standards platforms like GlobalSpec .

: Letters explicitly direct the installer which side of the aircraft structure must host the preformed factory head: