Wilson Electronics Dual Band  21.5 inc RV/Trucker Cellular Antenna Kit with Mount Powerful High-Gain Cellular Antenna Designed Specifically for Use with Rvs, Trailers, Campers & Other Non-Metallic Bodied Vehicles Built-In Spring Reduces Impact Damage Antenna Height Measures 21.5" Built-in spring reduces impact damage No ground plane required Built for RV use but works on Trucks as well. Easy to install and comes with 3 way Stainless Steel Mount. Standard CB 3/8 inch x 24 thread