What type of nut has notches cut into one side?

The correct identification of the nut with notches cut into one side is the castellated nut. This type of nut is designed specifically for use with a cotter pin or safety pin, which is inserted through a hole in the bolt or screw that passes through these notches. The notches serve as slots or grooves that allow the cotter pin to engage securely, thereby preventing the nut from loosening due to vibration or movement.

The design of the castellated nut makes it particularly useful in applications where safety and security are paramount, such as in automotive and aerospace settings. By engaging with the cotter pin, it helps to maintain tension and prevents accidental disengagement.

Other types of nuts, such as the wingnut, typically feature wings for manual tightening and do not have notches. Hex nuts are standard shaped and depend on torque for fastening, while locknuts utilize various designs to resist loosening but also do not incorporate notches like the castellated nut does. Understanding the specific characteristics and intended functions of these nuts is crucial for proper assembly practices in aerospace mechanics.