Just got the adaptors today and they are not the same as what ships with the Z3100. They are 3 inches and you can force them to fit on the spindle, but they are obviously spec'd for different printers. HP emailed with another part number Q1271-60629 that they said is the correct one for the Z series. They are shipping it out free of charge and don't want the wrong ones back. My lucky day I suppose.
The HP web site provides no information for that part number, and fails to list the printer that the part is used for.
Have you received Q1271-60629 yet? Is it the correct part?