These printers use the Q3964A cartridge:

HP Color LaserJet 2550

HP Color LaserJet 2550 L

HP Color LaserJet 2550 LN

HP Color LaserJet 2550 N

HP Color LaserJet 2800

HP Color LaserJet 2820

HP Color LaserJet 2820 All In One

HP Color LaserJet 2830

HP Color LaserJet 2840

HP Color LaserJet 2840 All In One