Which type of restraining device is authorized for use by SPs?

The correct choice, metal chain-link handcuffs, is recognized as an authorized restraining device for Security Personnel (SPs) due to their durability, reliability, and effectiveness in restraining individuals during potentially volatile situations. These handcuffs are designed to securely confine a person's wrists while allowing for a level of control that is essential for the safety of both the personnel and the individuals being restrained.

Chain-link handcuffs are generally considered standard equipment because they are made of strong materials that can withstand attempts to escape. Additionally, they provide a level of assurance that the device will hold under stress, which is critical in security contexts. Their ease of use in quickly immobilizing an individual also makes them favorable compared to other types of restraints that may require more training or are less effective in urgent situations.

While other options, such as plastic handcuffs and zip ties, might be used in specific circumstances for temporary restraints, they are not typically seen as appropriate for ongoing uses due to concerns about security and potential escape. Soft restraints, on the other hand, may not provide the necessary level of control expected in law enforcement or security scenarios, making them less desirable for authorized use by SPs.