Which item is used for correctly anchoring systems into hard surfaces?

The expansion shield is specifically designed for anchoring systems into hard surfaces such as concrete or masonry. It operates by expanding when a fastener is driven into it, creating a secure grip within the drilled hole. This anchor provides the necessary holding power in tough materials, making it ideal for situations where strong, reliable anchoring is crucial.

In contrast, the other options serve different purposes. For example, an extension typically refers to a tool or accessory that adds length, such as an extension cord or scaffolding extension, and does not contribute to anchoring structures. A dust mask is a protective gear worn to filter out dust and particulates from the air, which is unrelated to anchoring systems. An eye bolt, while it is a type of fastener that may be used for anchoring, is typically intended for securing cables or ropes rather than for anchoring into hard surfaces effectively. Therefore, the expansion shield is the most appropriate choice for anchoring systems into hard surfaces.