Keystone retaining wall blocks by Nicolock Paving Stones are the key to your next hardscaping project. The Compac® III system features Keystone block dimensions of 8 inches tall by 18 inches wide by 12 inches deep. The triangular receiving holes make assembly simple and can be used for near vertical or angled setback wall designs. Despite their large size, Keystone retaining walls can also make tight curves for added versatility.