it'll be moulded into the back of one of the webs between the spokes, just below the hole -- probably on the same spoke as the complete size designation ("15 X 6 1/2 JJ ET 21.5"). Note that M-B puts this on the BACK of the rim, so you have to take the darn thing off the car to read it, unless you're really skilled with one of those little mirror-on-a-stick gadgets. SAAB and BMW put the designations right on the outside, in the bolt circle area.