Harbor Mate Marine Accessories Double Trumpet boat horns are a great way to notify and warn nearby traffic quickly. The side-by-side 18. 5"L mount double trumpet design features (2) 4"D horns capable of blasting 109 dB powered off a 12V DC connection. Each package includes a 4"D double boat horn with mounting brackets, vibration reduction gaskets, and a 10. 5"L wiring harness for installation. Front mounting brackets slide along the horn shaft for custom fitting. Air horn is ideal for marine use and works great for RV"s and trucks too! Made with durable stainless steel construction for long lasting durability out on the water. Mounting hardware is not included - Due to various boat material compositions it"s best to check with the boat manufacturer for proper fastening hardware. Rear mounting bracket is diamond shaped measuring 5"L x 2. 5"W with (2) 0. 25" and (1) 0. 3125" mounting holes. The front bracket is 0. 75"D with a single 0. 1875" mounting hole. 109 dB Double Trumpet Stainless Marine Boat Horn (12 Volt) * 109 Decibels notifies and warns nearby traffic * 12 Volt DC connection includes 10.5"L wiring harness * Vibration reduction mounting gaskets * Double 4"D horn trumpets, side-by-side mount * Polished stainless steel construction