Fastener threads should always be loaded in which mode?

• A. Tension
• B. Compression
• C. Bending
• D. Torsion

Answer: (A)

Loading fastener threads in tension is what creates the clamp that holds parts together. When you tighten a bolt, it is stretched slightly, producing axial preload that pulls the joined surfaces together and resists external separating forces. This tensile load uses the bolt’s strength along its axis and keeps the thread engagement working to maintain clamping. If the threads were loaded by compression, bending, or torsion, the stress would concentrate in less favorable ways at the thread roots, increasing the risk of stripping or failure. So, the best way to load threads is in tension to maximize reliability and maintain the clamping action.