These are Micro Engineering HO scale Code 83 to 70 slide on plastic insulating rail joiners. These insulating joiners are perfect for where you want to electrically isolate sections of track when transitioning from Code 83 to Code 70 rail.
The Micro Engineering Company was founded in 1964 and over the years has become one of the leading companies in the US manufacturing model railway accessories. They started of producing scale model railway track in a single gauge then expanded this into a long line of track and track accessories in HO, N, G and O gauge scales. They then branched out into a wide range of highly detailed injection molded styrene kits including buildings, girder bridges, trackside accessories and much much more.