The Phelps Plastic AMP Vertex Series Diaphragm Elk Call 3PK use a "Flat Dome" for people who don't desire a dome style call, but enjoy the consistency and forgiveness a dome provides. The Vertex excels at cow vocalizations and can make bull sounds as well. 3 calls equipped with 3 different latex thicknesses and stretch options to match your calling preferences. FeaturesVertex 1: Light Build = Light Air Pressure Vertex 2: Medium Build = Medium Air Pressure Vertex 3: Heavy Build = Heavy Air Pressure