The Canon Roll Unit RU-42 is an accessory, not a standalone product — a roll-media feed unit that attaches to a compatible Canon large-format printer/plotter to let it print onto continuous roll paper instead of (or in addition to) cut sheets. Roll units like this are used in CAD, GIS, poster and technical-drawing print environments where long or continuous-length prints are common, and typically add automatic roll-feeding and cutting capability to the base printer. This listing doesn't specify which Canon printer model(s) the RU-42 is compatible with, so buyers should confirm fit against their specific printer before ordering.