Rock grips come in a set of 12. Plastic blow molded Rocks are molded from polyethylene with UV and cold weather protection. These come in 3 different shapes and are roughly 5 1/2″ x 4 x” x 2″. There are two to different sizes of mounting holes. The attaching screws and bolts are not included. Now smaller sized with the bolt holes that are 3/8″ and 2″ center to center. This product should last 2 years in harsh conditions and up to 5 years in optimal conditions. Some conditions may require replacement sooner.