Abstract: A plastic film cutter for clamping to an upstanding edge of a carton housing a supply of plastic film. The film is pulled across the top of an elongated cutter body which has a groove to guide a sliding cutter. The lower portion of the cutter has a plurality of inverted "U" shaped clamps for fitting over the carton edge. At least one of the clamps has a projection on its inner surface to prevent the cutter from being used on cartons for which it is not intended, that is, cartons which do not have a corresponding cutout to receive the projection.