This "BEHEMOTH" Train Air Horn dimensions are 12.3''" H x 11.25" W x 15.60" L. The Trumpet outlet diameters is a monster 6.25 INCHES. This horn includes anti-vibration mounting pad and all the mounting hardware needed to install. The solenoid will work on 12v or 24volt. This beauty not only looks GREAT, it is loud and ear piercing!! The rust resistant chrome plated trumpets will last for years to come. This purchase does not include air source needed for horn. See our on board air system/horn packages in our store. You will love this product, we sure do!!