How is a bolt marked with an X inside a triangle classified?

A bolt that is marked with an X inside a triangle is classified as a NAS close tolerance bolt. This marking signifies that the bolt adheres to specific tolerances and dimensions established by the National Aerospace Standards (NAS). Close tolerance bolts are designed for critical applications where precise fit and performance are vital, especially in aerospace and high-stress environments.

This classification also indicates that the bolt has undergone rigorous testing to ensure it meets aviation industry standards, providing assurance regarding the reliability and performance necessary in high-stakes situations.

In contrast, other classifications such as military specification bolts, Grade 5 bolts, and standard bolts do not necessarily imply the same level of manufacturing precision or the specific standards set by NAS. Military specification bolts are regulated under different criteria, Grade 5 bolts are a classification based on strength and material properties but lack the specialized tolerances, and standard bolts do not meet the stringent requirements needed for aerospace applications.