HP 656C printer question
 

This isn't specifically a Linux question but I feared that if I posted it in the "General" forum it wouldn't be read.

I just bought an HP Deskjet 656C off ebay to replace a malfunctioning 682C. I chose the 656 because it used the same color cartridge as the 682 did and because the cartridges were still good, I thought I'd be able to use them. When I got the 656 I found that the color cartridges are in fact the same, but the black cartridge is a 20, while the 682 uses a 29. Upon closer inspection the cartridges appeared identical except for a slightly different cap. I snapped the 29 into the 656 and it prints just fine.

Does anyone know if the 20 and 29 are supposed to be the same? Is there any risk of damaging the 656? On HP's site, the 20 is listed as being compatible with the 656, not with the 682, while the 29 is listed as being for the 600C Series. It appears to me that the 29 is the "economy size" version of the 20.

thanks...