These printers use the LC31C cartridge:

Brother IntelliFax 1820 C

Brother IntelliFax 1820 C Fax

Brother IntelliFax 1920 C

Brother IntelliFax 1920 C Fax

Brother IntelliFax 1920 CN

Brother MFC 3220 C

Brother MFC 3320 C

Brother MFC 3320 CN

Brother MFC 3420 C

Brother MFC 3820 C

Brother MFC 3820 CN

Brother PPF 1920 CN