Due to copyright and revision control, you cannot legally download the latest NAS523 PDF for free from random file-sharing websites (like PDF0 or DocSharing sites). Using an obsolete revision from 1985 could cause a catastrophic design failure.
A "captive" washer (NAS523) is pre-assembled onto the screw or bolt and cannot be removed without damaging it. A "free" washer (like AN960) slides on and off. Do not substitute one for the other; captive washers are used for high-vibration environments like engine cowlings. nas523 pdf
| Feature | NAS523 | NAS412 | AN960 | | :--- | :--- | :--- | :--- | | | Non-Metallic (Nylon, Teflon) | Metallic (Steel, Corrosion resistant steel) | Metallic (Aluminum, Brass, Steel) | | Washer Type | Captive (retained on screw) | Flat | Flat / Countersunk | | Primary Use | Insulation, Anti-vibration, Sealing | Structural joints, High load | General aviation, Low cost | | Plating Req. | Not applicable (non-metal) | Cadmium or Zinc | Cadmium or Phosphate | Due to copyright and revision control, you cannot
Rivet Identification Chart | Rivet Head Styles and Markings - Rivets Online A "free" washer (like AN960) slides on and off