This genuine replacement drum unit has been expertly designed for use with your Brother laser printer. The DR3115 Drum Unit ensures that your printer’s able to continue delivering top quality results, ensuring your important documents are reproduced with all the clarity they deserve. Brother laser printers require both a drum unit and a toner cartridge. The toner cartridge contains powder (toner) used for creating letters and images. The drum unit transfers the toner to the paper. You need to replace the drum unit when the printer displays the “replace drum” error message.