Keystone Hardscapes 83000 4" Anchor™ Diamond Pro Stone Cut® Retaining Wall Cap Pewter. The Anchor™ Diamond® retaining wall stones continue to provide economy of effort in a structural, finished product. The patented rear lip facilitates construction and ensures proper alignment and a precise setback. The Anchor™ Diamond® Cap will add a sense of completion to the wall system installed in the distinctive straight or beveled face style and is available in a wide variety of colors and blends.