Year after year, these are our best-selling plastic anchors. CRL Plastic Screw Anchors are designed to be used with wood or sheet metal screws. Their multiple-ribbed construction ensures secure holding power in hard or soft materials, from concrete to plaster. They are available in two styles: The shoulderless anchors will fit flush to the surface, the type with shoulders keep the anchor from slipping through the hole. 3/16" and 1/4" (4.7 and 6 mm) sizes accommodate screw sizes from #4 through #10.