InkOwl Printhead Repair Tool for HP 88, 940 This printhead repair tool is used to purge air from the inside of your printhead. To find out if your printhead has air, weigh it on a precise scale. A properly functioning printhead weighs 60g (1.9oz). Any less than 57g (1.8 oz), and you should probably use this tool. NOTE: To use this tool, you will need some ink bottles for HP 88 or 940 (sold separately). If your printer is actually giving you and error that your printhead needs replacement, the only solution is to buy a new printhead from HP.