UPDATE: HP 92 / 93
The Hewlett Packard 92 and 93 seem like new cartridges but are actually based on previous HP cartridges in physical design (the cartridge container itself) and ink. These cartridges that are the same are as the 92 and 93 are the HP 94 & 96 black and HP 95 and 97 tri-color.
The differences between the newer cartridges (92 / 93) and the older (94/96 black and 95/97 color) is the amount of ink in the cartridges and the sponge material. If you are refilling the 92 pigmented black cartridge we recommend injecting very little ink into the cartridge as the sponge material is less dense then the previous cartridges using these inks and same physical containers. This injecting less ink is applicable to the 93 tri-color as well. How much ink should be injected into the cartridges? With the 92 black we recommend starting with only 5ml (5cc) for the refill. The 93 tri-color should have no more then 2ml (2cc) per color injected. Though more ink can be injected into the cartridges at a certain point of saturation the sponge material will no longer be capable of holding the ink. This will result in bleeding from the bottom of the cartridge. The cartridges will continue to release ink from the print head until equalization occurs and the sponge is capable of holding the remaining ink.
There are no additional differences with these cartridges and in some printer models these cartridges can be used interchangeably.

When refilling these cartridges use the fill hole closest to the contact points of the cartridge.


UPDATE: HP 21 / 22
The Hewlett Packard 21 and 22 seem like new cartridges but are actually based on previous HP cartridges in physical design (the cartridge container itself) and ink. These cartridges that are the same are as the 21 and 22 are the HP 27 & 56 black and HP 28 and 57 tri-color.
The differences between the newer cartridges (21 / 22) and the older (27/56 black and 28/57 color) is the amount of ink in the cartridges and the sponge material. If you are refilling the 21 pigmented black cartridge we recommend injecting very little ink into the cartridge as the sponge material is less dense then the previous cartridges using these inks and same physical containers. This injecting less ink is applicable to the 22 tri-color as well. How much ink should be injected into the cartridges? With the 21 black we recommend starting with only 5ml (5cc) for the refill. The 22 tri-color should have no more then 2ml (2cc) per color injected. Though more ink can be injected into the cartridges at a certain point of saturation the sponge material will no longer be capable of holding the ink. This will result in bleeding from the bottom of the cartridge. The cartridges will continue to release ink from the print head until equalization occurs and the sponge is capable of holding the remaining ink.
There are no additional differences with these cartridges and in some printer models these cartridges can be used interchangeably.

When refilling these cartridges use the fill hole closest to the contact points of the cartridge.