Abstract: A valve stem adaptor is provided for a valve stem assembly having a body with a first end and a second end and having an elongated shaft portion with a first end and a second end and having a passageway extending through the shaft. The shaft second end has external threads displaced thereon, and the body second end has a circular end rim with an end rim groove extending around an end rim perimeter. A fastening mechanism engages an outer surface of a tire rim. The valve stem adaptor includes an adaptor body manufactured from rigid material and has an adaptor rim portion with an upper surface, lower surface and passageway extending through the adaptor body. The valve stem adaptor also includes a first O-ring adapted to fit adjacent an upper surface of the adaptor rim portion, and a second O-ring adapted to fit adjacent a bottom surface of the adaptor rim portion.