A triangle on the head of a steel bolt indicates which of the following?

• A. A bolt with a triangle on the head indicates a high-strength bolt.
• B. Close tolerance bolt.
• C. A bolt with a square head.
• D. A bolt used for aerospace standard.

Answer: (B)

In aviation fasteners, head markings convey important properties such as tolerance and fit. A triangle stamped on the bolt head identifies a close-tolerance bolt. These bolts are manufactured with tighter dimensional tolerances for diameter and length, which is important in assemblies where precise alignment and snug fits are required to maintain proper preload and function. So, the triangle mark signals that this bolt is a close-tolerance type, not simply a high-strength grade, a square-headed bolt, or an unspecified aerospace standard.