These Extra Large 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. There are two sets of each 3 different shapes. There are 6 rocks 6 x 4 x 3” and six sets of 6 x 5 x 3” There are two holes per rock 3” center to center One set of two rocks of the 6 x 5 x 3’ requires two different sizes of mounting screws and washers. The one side of the two holes requires a 3/8” x 1 ½” screw or bolt and washer The other side requires one #14 screws or bolts x 1 ½” and washer The other 10 rocks all require two each #14 screws or bolts by 1 ½” and washers. The attaching screws or bolts and washers are not included. This product should last 2 years in harsh conditions and up to 5 years in optimal conditions. Some conditions may require replacement sooner.