NEIEP Mechanics Practice Exam

What type of locking device uses a second nut against the first to secure it when tightened?

1. Set screw

2. Lock washer

3. Jam nut

4. Retaining ring

The correct answer is: Jam nut

The correct answer is that a jam nut is a type of locking device that utilizes a second nut against the first to secure it when tightened. This arrangement creates a secure connection by preventing the primary nut from loosening due to vibration or other external forces. When a jam nut is tightened against the primary nut, it increases friction between the two, effectively locking both in place. In applications where vibration might cause components to loosen, using a jam nut provides an effective solution to maintain tightness without the need for additional locking mechanisms. This method is especially useful in machinery where maintenance access is limited, making it beneficial to have a simple yet effective locking method. The other options do have their unique functions but do not employ the same double-nut approach as the jam nut. A set screw typically secures an object in place without other components but doesn't utilize a second fastening piece as a jam nut does. A lock washer is designed to prevent loosening through spring tension and may deform under pressure but does not use two nuts. A retaining ring serves to hold components on a shaft or in a housing and does not involve nut-based locking.