For the order number (Order No.) of the drum unit, please refer to the User's guide provided with your Brother Printer or the Consumables & Options page of your model on Brother Solutions Center. To visit Consumables & Options page, click your model name link (e.g. HL-XXXX * ) on the top section and then click "Consumables & Options" link on the opened page. * XXXX stands for your model name.