What action must be taken to ensure a proper fit when using handcuffs?

The correct action to ensure a proper fit when using handcuffs is to double lock the handcuffs. This step is crucial because it prevents the handcuffs from tightening further during movement, which can cause injury or excessive discomfort to the individual being restrained. Double locking the handcuffs ensures that they remain at a consistent size, providing safety for both the detainee and the officer. This practice also helps to prevent potential escape attempts, as it limits the ability of the subject to manipulate the handcuffs.

While ensuring the handcuffs are tight around the wrists may seem important for security, it is more critical to achieve a balance where the restraints are secure yet comfortable enough to prevent injury. Conducting a body search first is a necessary procedure for officer safety and to recover any potential weapons or contraband, but it does not directly relate to the fit of the handcuffs. Lastly, placing handcuffs on a subject's ankles is typically reserved for specific situations and is not standard practice for securing an individual in a way that ensures proper fit and safety for handcuffs.