What keeps a bolted joint tight?

• A. Lock washers or safety wire
• B. Elastic stop nuts
• C. Anaerobic sealer
• D. Adequate torquing/stretching of the bolt

Answer: (D)

Generating preload through proper torquing keeps a bolted joint tight. When you torque a bolt to the specified value, the bolt stretches slightly and pulls the joined parts toward each other, creating a clamping (preload) force. That clamp presses the parts together and generates friction in the threads and under the bolt head, which resists loosening from external loads and vibration. If the preload is insufficient, external forces can separate the parts and the joint can back off. Over-torquing can yield or damage parts, also compromising tightness. So the key to maintaining a tight joint is achieving and maintaining the correct preload by tightening the bolt properly.

Other methods like lock washers, safety wire, or nylon-containing nuts can help resist loosening in some cases, and sealants may lock threads or seal, but they don’t replace the essential preload that actually keeps the joint tight.