Itn’t the G-520 = 8", G-540 = 9" and G-560 = 12" ?
http://20cheaddatebase.web.fc2.com/needie/NDGRACE/GRACE.html
For a normal arm, the second digit of the three-digit number of the model number is a guideline for the length. For example, in terms of length, G-520L <540L <560L.
http://20cheaddatebase.web.fc2.com/needie/NDGRACE/GRACE.html