What would cause uneven brake pad wear?

[Nato]

I've just gone out to the car to check what type of pad is on the rear, and I've noticed that the pads have worn unevenly. The n/s pad has a few mm left on it, but the o/s pad is down to the metal, which has been causing the grinding noise which made me think I needed to do brakes all around. The front pads look nearly new. What would cause the uneven wear on the rear pads?

Also, when I went to buy pads from my local factors, they told me there are two different types of pad for the rear - one with a pin that loops through the top, and then another that looked totally different. Can anyone shed any light on this?

[hoochydady]

yip u ethere have a cheap set of pads on it or not the rite 1s or u need to do ur discs to they may have been to worn and this has shortend the life of the pads

[m8internet]

Uneven pad wear is very common, especially towards the end of their life
A few mm is nothing
I would be more concerned if one surface had at least 25% of the material remaining and three were worn to the last 2mm

[shearzy]

they all wear un evenly i think, all my cars iv had have done

[carpet]

If the pads are worn uneven to any great extent the problem could be the caliper sticking on the guide pins. These are the pins that the caliper mounts/runs on that you undo and remove to replace the pads. Apply some grease and ensure that the calipers move freely when you replace them.