What type of threads may some fasteners used on rotating elements of machinery incorporate to prevent loosening?

• A. Right-hand threads
• B. Left-hand (LH) threads
• C. Coarse thread standards
• D. Self-locking threads

Answer: (B)

When parts rotate, the twisting motion can cause fasteners to back off if a standard right-hand thread is used. Left-hand threads reverse the direction of tightening, so the rotation itself tends to tighten the joint rather than loosen it. This makes them a practical choice for fasteners on rotating elements where the rotation direction is predictable, helping maintain a secure connection. Right-hand threads would more likely loosen in that same motion, coarse thread standards don’t specifically address anti-loosening behavior, and self-locking threads rely on friction or inserts rather than the thread direction itself.