Whenever a situation calls for placing both ends of a sling into a hook or placing more than one sling into a hook, what piece of rigging hardware should be used?

Using a shackle when dealing with both ends of a sling or multiple slings into a hook is the preferred choice because it is specifically designed to connect different rigging components securely. Shackles are robust pieces of hardware that can handle significant loads, and they feature a pin that goes through an opening to create a reliable connection. This design helps in maintaining stability and ensuring that the load is distributed evenly across the slings involved.

In situations where multiple slings are being used, a shackle provides a reliable and tested method for combining those slings so they can effectively lift loads without any risk of slippage or disconnection. This capability is critical in overhead lifting scenarios where safety and stability are paramount.