The defining feature of the NAS523 is its head geometry. Unlike a standard 12-point or hex head bolt, the NAS523 head is designed to minimize the "wrenching diagonal"—the distance measured across the corners of the head.
Provides instructions for hole preparation, such as D for dimpling, C for countersinking, or D2C (dimple two sheets and countersink the third). nas523 pdf top
. For instance, "D2C" means dimple two top sheets and countersink the third. Southeast (SE - Bottom Right): Specifies the fastener length or grip, often in inch increments. Key Identification Resources The defining feature of the NAS523 is its head geometry