Originally Posted By: Canadastang
Not to mention that a lot of parts mfr's will have multiple grades of parts.
A friend of mine toured a TRW factory way back in the day and he was saying they had grade A stuff that was of top tier quality for OEM and high quality aftermarket, then grade B stuff for jobbers/OE equivalent, then grade C for economy grade parts, reboxers etc.
Not sure if this is still the case.
It's a standard practice that was adopted to accommodate tool wear and it is definitely being used today, probably more than before. Brand new tools produce the most accurate batch and that goes to OEMs. As the tools wear out, they produce parts with more tolerance variations. That's why parts are grouped by grades, because it signifies the batches that were made using that specific tool. The more batches, the less accurate and consistent the parts produced in that batch get.
Dies, diamond grinding stones and various cutting tools are very expensive, this way their lifespan is maximized.