These printers use the X644X21A cartridge:
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