HP No 88 Black/Yellow Printhead. For HP Officejet Pro K550 inkjet printers. OEM Ref - C9381A. The HP No.88 Black/Yellow Printhead is the perfect product for ensuring that your machine is working at its best possible level. HP consumables are developed in close proximity to HP machines, ensuring that they work together without any problems, achieving quality prints with every use. Easily installed into your machine, you don't need any specialist knowledge in order to make the most from your printer.