Tecnigas GP4 Exhaust for QMB139 50cc Engines.The Tecnigas GP4 exhaust is an eye catching nickel plated GP racing styled exhaust designed specifically for the QMB 50cc 4 stroke engine. Head Pipe Bolt Hole Spacing: 50mm Head Pipe Inner Diameter: 19mm Includes Mounting Hardware, Gasket and Instructional Booklet