Bolt grade can be determined by

• A. The length of the bolt
• B. The color of the bolt
• C. The marking on the head of the bolt
• D. The material of the bolt

Answer: (C)

Understanding bolt grade means focusing on strength and how the bolt is made, not its size, color, or just what material it started as. The grade is shown directly on the bolt head with markings that identify the strength class. Those head markings tell you the specified mechanical properties, such as tensile strength and hardness, which define how much load the bolt can safely handle. For example, SAE grades like 5 and 8 or metric grades like 8.8 and 10.9 are all conveyed by specific marks on the head, reflecting heat treatment and alloy composition tailored to reach those strength levels. The length or color of the bolt doesn’t indicate its grade, and while the material matters, the same material can be finished at different strengths; the head markings uniquely communicate the grade. So, the marking on the head is the reliable way to determine bolt grade.