How many lines are on the head of an SAE grade 8 bolt?

The correct answer regarding the number of lines on the head of an SAE grade 8 bolt is six. This is a key identifying feature of SAE grade 8 bolts, which are distinguished by their high strength and are often used in demanding applications. The six lines represent that the bolt meets the specifications of a grade 8 fastener, which means it has been tested to a minimum tensile strength of 150,000 psi.

Understanding these markings is crucial for ensuring that the correct type of bolt is used in specific applications, as using the wrong grade can lead to mechanical failure. Other grade bolts have fewer lines; for example, a grade 5 bolt has three lines and a grade 2 bolt has none. Knowing these identifiers not only helps in distinguishing between grades but also reinforces the overall knowledge of fasteners and their strengths in engineering and construction contexts.