The Jon Boat Gunwale Base is designed to fit Jon Boats with Monster Rod Holders products or any Rod Holder that is 1/2″ in diameter and Right-Hand Threading. This Monster Rod Holder product is a Rod Holder base that is specially designed to fit the small gunnels on Jon Boats. Fits most sizes and can also be used on the 7/8″ and 1″ round utility rail.Dimensions:Width: 1″Length: 2 1/4″Height: 5/8″