These printers use the X644H21A cartridge:
Click On a Printer to View it's Cartridges

          Lexmark Clinical Assistant
          Lexmark Clinical Assistant MFP
          Lexmark EDUCATION STATION
          Lexmark Legal Partner
          Lexmark Legal Partner MFP
          Lexmark X 642 E
          Lexmark X 644 E
          Lexmark X 644 E MFP
          Lexmark X 644 EF
          Lexmark X 646
          Lexmark X 646 EF MFP
          Lexmark X 646 DTE MFP
          Lexmark X 646 E MFP
          Lexmark X 646 EF