These printers use the W2121X cartridge:

HP Color LaserJet Enterprise M-554 DN

HP Color LaserJet Enterprise M-555 DN

HP Color LaserJet Enterprise M-555 X

HP COLOR LASERJET ENTERPRISE FLOW MFP M-578 C

HP COLOR LASERJET ENTERPRISE FLOW MFP M-578 E

HP COLOR LASERJET ENTERPRISE FLOW MFP M-578 Z

HP COLOR LASERJET ENTERPRISE MFP M-578 DN

HP COLOR LASERJET ENTERPRISE MFP M-578 F

HP Color LaserJet Enterprise MPF M-578 DN

HP Color LaserJet Enterprise MPF M-578 F