6The exhaust system (e.g., muffler) is not equipped with this engine as standard.When you select the exhaust system, check the engine speed (rpm) when themaximum output is generated by using the exhaust system you are going to select.And then decide the appropriate screw-propeller that would meet such enginespeed (rpm) that the exhaust system requires.In general, standard size of the screw propeller (Surface prop type) are as follows:Pitch ratio ( mm )1.9 ~ 1.4Diameter ( mm )65 ~ 754. Screw-Propeller