These printers use the 74C1SK0 cartridge:
Lexmark CS 720
Lexmark CS 720 DE
Lexmark CS 720 DTE
Lexmark CS 725
Lexmark CS 725 DE
Lexmark CS 725 DTE
Lexmark CX 725
Lexmark CX 725 DE
Lexmark CX 725 DHE
Lexmark CX 725 DTHE