What is the primary characteristic of a lock nut?

• A. It is designed to be tightened by hand
• B. It has internal threads with an insert to prevent loosening
• C. It has a significantly large surface area
• D. It is primarily used with flat washers

Answer: (B)

The primary characteristic of a lock nut is that it has internal threads with a design that incorporates an insert or mechanism that helps prevent loosening under vibration or stress. This feature is crucial in applications where maintaining tension and integrity of the connection is vital, such as in machinery or automotive components. The locking mechanism can be achieved through various designs, including nylon inserts, mechanical interlocks, or other means that create friction against the bolt or screw it secures.

The other options do not accurately represent the defining qualities associated with lock nuts. For instance, tightening the lock nut by hand does not characterize its function or necessity. While surface area can be important in some contexts, it is not a primary factor in defining what makes a lock nut unique. Additionally, though flat washers may be used in conjunction with various types of nuts, they are not a defining feature of a lock nut itself and do not contribute to its specific purpose.