The Double Mount is the best on the market today with many adjustments to fine tune your setup. Made of high strength 6061 aircraft aluminum. The depth finder mounts are tapped for Humminbird,Garmin and Lowrance (WILL NOT FIT HELIX 7 model) and will handle 7″ to 16″ wide depth finders. The picture with the ruler shows the height of each set of arms. This is a 12″ arm setup. The top plate is 17.5″ from the base.