CISS-4G is the most efficient CISS cartridge. The 4G works exactly same as the original HP Officejet Pro 8600/8100/6600's working system. So, it makes possible the Head Cleaning Process of the original HP printer's have. (Other cartridges can't do this.) I'm telling you that it is only CISS-4G to make possible the process. If you contact us E-mail : inktown7@naver.com Homepage : www.printerbuy.co.kr Phone : 82-10-9996-8727