Is there a specific regulation for the maximum tolerance allowed while manufacturing brake pads? If not, what is a usual value set by manufacturers? I would really appreciate references. Thanks a bunch!
There may be different specs for various makes and models, but here is what I look for:
If wear is even, and pad is squarely wearing, when it gets just under 1/8" or 3mm, I get replacement pads and put them on. I may not actually get them on until 2mm, but 3mm is the trigger point to go get the parts.
If wear is not even, the most worn side must have 3mm. Getting to the pads, and resolving sticking pins, or whatever is causing the uneven wear is a high priority because I don't want the backing metal to contact the rotor.
My guess is that the manufacturer specs are smaller than my guidance, because I am conservative. Some brakes with expensive pads, like aircraft brakes, do have smaller tolerances, but in general they are only lightly used, and they are readily inspected prior to each flight.
On the daily driver or family car, I try to inspect brakes every month or two in the nice weather, and try to do each month in the winter. The reason for more frequent checks in the winter is that some municipalities use sand and coal cinders as abrasives for winter driving. These materials can get stuck more easily in the brake mechanisms, and cause sticking of the pads or pins. Also road salt and aggravate corrosion of the pads especially near the end of winter when temperatures are higher (faster corrosion) and there is frequently more slush pushing aggregates into the brake mechanisms. Inspection can often be done with a mirror, so you may not need to have to jack up the car and pull the wheels off.