A diamond indicates .090" cast iron sleeves. You will only see the diamond on 8N's with a serial number after 433578. All earlier models have the stars. The format for the serial number is *8N12345*. All serial numbers will begin with either 9N or 8N.
A diamond symbol denotes the beginning and end of the serial number. This photo shows a
model 850 (800 series) with serial 93706 (1956).