Steel drop-in anchors are an internally threaded expansion anchor used in solid concrete, hard stone, and solid block. Some applications are suspending conduit, fire sprinklers, strut and cable trays, pipe suppors, and suspended lighting. A hole is drilled to the same size as the outside of the anchor, it is dropped in flush or just below the surface, and a fastener is screwed into the internal threads causing the anchor to expand and hold in placed. Made of zinc plated steel for strength and mild corrosion resistance.