PHANTOM X 5.5: Designed to promote a more flowing "blade-like" feel with the stability benefits of a mallet Solid face/body precision milled from 303 stainless steel Integrated aluminum sole plate and customizable steel sole weights Combination of heavier steel and lighter aluminum moves weight to perimeter of head for increased MOI, stability and forgiveness Arc-enhancing small slant neck Milled sight line on the topline for alignment