Double expansion anchor is also called double expansion shield. The body is made of a die cast alloy called zamak, which has good corrosion resistance. The anchor is used for light duty to medium duty In softer material, or a material whose strength is suspect, the anchor is a great fastener. It is made up of six parts: two halves of the anchor body, one threaded expansion nut, one non-threaded expansion nut, and two spring steel rings. The anchor body is expanded to against the base material when a bolt is threaded into the double expansion anchor.