HP +Referral+
U4778E
is compatible in the following HP Models:
HP Deskjet 3500 Printer series
HP DESKJET 3520V INKJET PRINTER - C8994B
HP DESKJET 3520W INKJET PRINTER - C8994D
HP DESKJET 3550V INKJET PRINTER - C8991B
HP DESKJET 3550W INKJET PRINTER - C8991D