The core size is indicated since roll printers have specifications for core size. If you are not printing on these labels, then you would not need to worry about the core size. If you are using a printer, please refer to your printer's manual or specification sheet to see which core size is needed. If you are unable to locate this information, you can confirm your printer's make and model with our Customer Support Team by calling 888-575-2235. We will be happy to research this information for you.