These printers use the Q6511XX cartridge:

HP LaserJet 2400

HP LaserJet 2410

HP LaserJet 2420

HP LaserJet 2420 D

HP LaserJet 2420 DN

HP LaserJet 2420 DTN

HP LaserJet 2420 N

HP LaserJet 2420 TN

HP LaserJet 2430

HP LaserJet 2430 DTN

HP LaserJet 2430 N

HP LaserJet 2430 T

HP LaserJet 2430 TN

TROY-Systems Troy 2420

TROY-Systems Troy 2420 /T

TROY-Systems Troy 2420 D/DTSECUEX

TROY-Systems Troy 2420 D/DTSECURE

TROY-Systems Troy 2430