This O₂ sensor mounting boss with an M18×1.5 plug is an aftermarket adapter part that allows you to add—or neatly plug—a mounting point for a lambda (O₂) sensor on a compatible exhaust manifold or muffler, designed for Honda Ruckus models equipped with GY6 engines.
The term "stepped mounting boss" refers to a machined surface with an M18×1.5 thread pitch, the standard for lambda sensors. The stepped design ensures a proper transition between the internal diameter of the exhaust pipe and the sensor mounting area, while also providing a mechanical and thermal seal when a plug is installed.
Its main function is to:
provide an M18×1.5 threaded base for mounting an O₂ sensor
allow for the installation of a sealing plug when no sensor is used
ensure a clean and secure connection between the exhaust and the sensor (or plug)
reduce exhaust gas leaks at the mounting point
This boss is particularly useful in custom aftermarket setups where the exhaust is not stock or does not have a designated O₂ sensor port, but where adding (or removing) a sensor is desired.
