Maximum extension size: 18 inches high by 56 inches wide Minimum extension size: 12 inches high by 34 inches wide. May not work in all vehicles please measure your space. Made from high-quality powder-coated steel for medium to large dogs. not recommended for small dogs as they can slip thru the bars Vehicle must have adjustable headrest poles for the mounting to work, it will not work with fixed headrest. Please tighten clamps firmly. It will not work in vehicles that have an additional seat belt box in the middle of the backseat. Removing the guard is easy, just loosen off the tightening knobs and remove it from the headrest posts. Contact us for replacement parts and help with installation our customer service sheet is inside the box