An ink jet head holder supported from a frame and includes a transversely movable rod supporting an ink jet print head with a similar print head holder on the opposite side of the frame. A conveyor for conveying an object having opposed print-receiving surfaces between the print heads. Longitudinal channels are supported by the frame on opposite sides of the conveyor. The print heads are supported on the longitudinal channels and side guide rails are also supported on the channels. The channels are laterally movable to vary the width of the path of packages on the conveyor. The side guide rails are also adjustable laterally relative to the print heads. The print heads have cam faces for contacting the packages at a predetermined transverse distance from the print head nozzles. Biasing means hold the print heads with the cam faces bearing against the print-receiving surfaces that are printed by ink from the nozzles.
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