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