They weren't free, at least in my case. (Cost about $10.00 for a set of four.) You use one on each rear brake pad. The Volvo parts guy told me they were a service campaign kit to eliminate rear brake pad vibration. Basically, they're metal shims with a cutout on one half. Half the brake piston contacts the shim while the other half directly contacts the pad backing. For about six months, my '94 850T had an intermittant but severe vibration that shook the whole car when braking from about 10 mph until stopped. I traced it to the left rear wheel by repeatedly braking from slow speed while an outside observer took note of where the noise was coming from. I changed the rotor once and the pads twice to no avail. Tried standard shims then no shims. The vibration usually went away for a day or so then came back as before. I was getting ready to order a new caliper, thinking it might be dragging and overheating. Not sure where I heard about the shims, but probably read it somewhere. Went to the dealer parts counter and said I'd heard about a shim that reduced brake vibration. Parts guy knew what i wanted and an hour later they were installed. (Just on the left side, still haven't got around to putting them on the right.) I haven't had even a hint of vibration since installing the shims.