Back Beat 16mm Release Prints
While certainly not a rarity, it's getting continually less use with greater reliance on inferior quality video in many places where 16mm film was standard.
The film base is 35mm wide but the perforations are sized and pitched to 16mm standards. Generally an internegative is created from two passes through an optical printer, then the 35-32mm film is printed from the IN. After printing, 1˝mm is slit from each edge and the remaining film is slit down the center to yield two 16mm reels. The soundtracks are dual-bilateral monophonic.