Our Best Selling Plastic Anchors Use with Wood or Sheet Metal Screws Without Shoulders 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 inch (5 and 6 millimeter) sizes accommodate screw sizes from #4 through #10.