These printers use the C540H1MG cartridge:
Lexmark C 540
Lexmark C 540 DW
Lexmark C 540 N
Lexmark C 543
Lexmark C 543 DN
Lexmark C 544
Lexmark C 544 DN
Lexmark C 544 DTN
Lexmark C 544 DW
Lexmark C 544 N
Lexmark C 546 DTN
Lexmark X 543
Lexmark X 543 DN
Lexmark X 544
Lexmark X 544 DN
Lexmark X 544 DTN
Lexmark X 544 DW
Lexmark X 544 N
Lexmark X 546 DTN
Lexmark X 548 DE
Lexmark X 548 DTE