Directly from autozone via my email:

PFC is introducing a new product into the market that offers
stainless steel shims, increased stopping power, and a improved street
compound to decrease dust and noise. We will carry it in all our stores. As
a result of the new product introduction the warranty on the current and
new product has been change to 2 years to avoid confusion. This is subject
to future change. It in no way reflects product quality. Thanks,
Brian Koffler
Under Car Team - Brakes
AutoZone Merchandising Dept.


ps: I think I saw this on the autozone comp...it's part number 502 but it was a special order.