Hollow Wall Anchors
Hollow wall anchors are a three-piece fastener consisting of a cylindrical expander shell with longitudinal sections of its shank removed. This design allows the shell to be pulled toward the head and form anchoring legs on the blind side of the assembly. The shell has a threaded opening at one end and a flanged collar at the opposite end with an opening sufficiently large enough to allow a screw to pass to the threaded opening. The flange of the collar has prongs which dig into the bearing surface at the front end of the assembly. The remaining pieces of the hollow wall anchor are the combo-drive pan head screw and either a fiber or steel flat washer.
Steel hollow wall anchors are considered to be light-duty anchors. They require a pre-drilled hole and may be used in drywall, sheetrock, plaster or paneling. When properly installed, they will not crack or crumble the wall material and resist vibration. The machine screw may be removed and inserted multiple times to accommodate an exchange of fixtures.