Outer width = 4″ (Actual Width 3 5/8″) Roller Outer Height = (Actual Height 2 7/8″) Roller Inner Height = (Actual Height 2 3/8″) Fits a 1/2″ Bolt Stoltz polyurethane is known for it's durablity, longevity and non marking material. This boat trailer roller is specifically designed for a boat that has a Semi V bow and a 4" wide roller mounting bracket. The Stoltz bow roller is made of a high end polyurethane material. This Includes (1) 4″ Semi V Center Roller. Our polyurethane material is built for all weather conditions.