The StyleWriter II ink cartridge (M8041G/A) is NOT compatible with the original StyleWriter.
The original StyleWriter ink cartridge (PN M8052G/A) is also not compatible with the StyleWriter II.
The visible difference between original cartridges and current ones are the colors on the label of the cartridge itself. The original label has a vertical blue stripe on the right side of the cartridge and a black Apple logo above the word "StyleWriter". There are two current versions of the black and white StyleWriter series ink cartridges.
Version 1
One of the new cartridges does not have the vertical blue stripe, however it has two arrows that point in the direction the cartridge should be installed. This cartridge has the Apple logo above the words Apple StyleWriter. The word Apple and the Apple logo are red on this version of the cartridge.
Version 2
The other new cartridge retains the blue vertical stripe, but contains the printers it is compatible with on the cartridge itself. Below the words StyleWriter, StyleWriter II, and Portable StyleWriter it says Black Ink Cartridge.
If you wish to determine which cartridge you have, check the color on the cartridge to see if it is red or blue. If there is a vertical blue line, it will list the printers it is compatible with. Do not attempt to use the cartridge on any printer that is not listed on the blue striped cartridge. If there is the red Apple logo on the cartridge without a blue vertical stripe, it is compatible with all three StyleWriter printers.
Summary of Ink Cartridge Part Numbers