Abstract: An adapter is disclosed for mounting an exhaust muffler onto a threaded exhaust port located at the external surface of an internal combustion engine. The adapter includes a hollow, cylindrical neck portion having screw threads formed on a first end thereof and circumferentially about the outer surface thereof, for threadably engaging the threaded exhaust port of the internal combustion engine. The adapter further includes a plate portion formed on a second end of the neck portion, having a central opening coincident with the hollow interior of the neck portion, with a first face proximate to the screw threads and a second face opposite to the first face. The adapter forms a seal between the external surface of the internal combustion engine and the first surface of the plate portion when the neck portion is operatively engaged with the exhaust port.