How to Choose the Right Hex Bolt for Your Project

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　　Hex bolts (hexagon head bolts) are the workhorses of the fastening world. However, selecting the wrong grade or thread type can lead to structural failure or stripped threads.

　　Understanding the Grades

　　The grade indicates the strength of the bolt.

　　Grade 2 (A307): Low carbon steel. Used for general household and low-stress applications. It is soft and easy to tighten by hand.

　　Grade 5: Medium carbon steel, quenched and tempered. Identified by 3 radial lines on the head. It has a tensile strength of 120,000 PSI. Ideal for automotive and machinery.

　　Grade 8: High carbon alloy steel. Identified by 6 radial lines. It has a tensile strength of 150,000 PSI. Used for high-stress structural connections (e.g., suspension systems).

　　Thread Pitch: Coarse vs. Fine

　　UNC (Unified National Coarse): The standard. Less prone to cross-threading and easier to install in dirty or damaged holes. Best for general fabrication.

　　UNF (Unified National Fine): Threads are tighter together. Used for precision adjustments, thin-walled materials, or where vibration resistance is needed (fine threads are less likely to loosen).

　　Length and Coatings

　　Measure length from under the head to the end of the thread. For outdoor projects, choose Hot-Dipped Galvanized (thick coating for maximum rust protection) or Stainless Steel (304 for general, 316 for marine environments).

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