These lag or expansion shields are used for fastening lag screws into fastening into wood and concrete. The expansion shield acts as an anchoring point into a concrete slab or foundation, expanding when the screw threads are engaged during installation. Common uses include frames, and outdoor play equipment. When used in conjunction with a lag screw it can also be used in many masonry applications. Use in pre-drilled hole. The length of a lag screw is measured from the underside of the head to the pointed tip of the screw.