ACDelco 503-637 Professional Premium Gas Charged Front Suspension Strut Assembly 1-3/8 inch bore piston with sintered iron construction for durability and longer service life Single lip oil seal for minimized friction Super-finished chromed piston rod reduces corrosion, ensures proper seal lubrication, provides a consistent wear surface, and assists in longer product life Precision engineered for top-of-the-line performance Drawn over mandrel (DOM) pressure cylinder for high quality sealing properties and reduced internal friction to assist with longer product life