in your house door lock there are "pins" shaped like this []
...........................................................................v
and they are round, in your car (many cars, incl. my mercedes, so probably more mbs too)
there are "wafers" that are [] square and very flat, they look like the 2 small items in the top of this picture
http://www.padandwheels.com/mr2/tails/removewafer.jpg
those are probably ford wafers, the mb ones are a little diffrent, some of the newer ones are split in two (to resist picking) but in my doorlock they are not split, but are diffrent in that there is a little nub on the inside of the hole in the center of the wafer so it looks like this
[--]
[...]
[-..] < nub here
[--]
that nub is so that the key can contact the wafer in the right spot because many of our mb keys are high-security (look at a mb key and if you notice the cuts are on the side of the key, not on the top, so it requires a special key machine to duplicate)
EDIT: ignore periods in ascii art.