F-18 4×4 and 4×2. Design features: Wheel propelled turners for paved (2×4) and unpaved (4×4) Economically priced. Simple control systems. Accept Frontier self-trailer packages. Frame Strength: 8″ x 12″ mainframe members with “ladder” construction minimize flex for self-trailer capability. Tunnel Lining: 3/8″ plate.