Hollow wall anchors or Molly anchors are designed to expand and grip as the screw is tightened in drywall, plaster or other hollow wall applications. These anchors are available in various wall thicknesses, therefore, check size designation on the package. Once installed the screw may be removed and re-installed as often as required. For drill type anchors, drill hole the size of anchor and install. For hammer-in type simply install by tapping in with a hammer.