What do aircraft bolts with a cross or asterisk marked on the bolthead signify?

Aircraft bolts that are marked with a cross or asterisk on the bolthead signify that they are AN bolts, which stands for Army-Navy bolts. This specific marking indicates that the bolts meet certain standardized specifications set for use in aerospace applications. AN bolts are known for their high strength and reliability, making them ideal for use in critical aircraft components.

The marking serves not only as an identification but also as a quality assurance measure, ensuring that the bolthead meets strict manufacturing and performance criteria essential for the safety and structural integrity of an aircraft. These bolts are often used in various applications where precision and durability are paramount, thus making them a fundamental choice in aircraft construction and maintenance.