Cotter pins must be used with all which type of pin shackles?

Cotter pins are specifically designed to secure the ends of pins and prevent them from backing out of their intended position. In the context of pin shackles, the correct answer highlights that cotter pins should be used with round pin anchor types. This is because round pin shackles rely on the pin being securely fastened to maintain strength and safety under load.

The round pin design typically features a hole on the end that is suitable for a cotter pin, providing an effective locking mechanism. When using a round pin anchor, the cotter pin prevents the pin from becoming dislodged, which could lead to catastrophic failure during lifting operations. Therefore, employing a cotter pin in conjunction with round pin shackles is crucial for ensuring a safe rigging and lifting procedure.

Other types of shackles, such as screw or safety pin shackles, may utilize different mechanisms for securing the pin and might not require cotter pins for secure operation. In these cases, the design of the shackle itself incorporates features that negate the need for additional safety pins. Hence, understanding the specific application and design of each type of shackle helps determine the appropriate safety measures, such as using cotter pins where necessary.