As a former NAPA supplier I can tell you without hesitation NAPA is picky about quality. They require that parts supplied to them meet OE fit, form and function. They know how to monitor quality and they check parts.
I will only comment that ALL manufacturing that I have worked in over the years (as an engineer) their are always different levels of quality. Using Intel as an example, all of the parts were manufactured and looked exactly the same but would electrically test and perform at different levels.
The Military and ATT at the time were tested to much higher standards & under more extreme conditions. The parts that failed those tests were then retested as commercial parts under less stressful conditions and standards. They were then categorized as Bin 1, 2, 3, 4 or 5 parts.
Bin 1's were higher priced of course and went to manufacturers that would pay for the higher quality (IBM, HP Etc)
Bin 2's A bit cheaper and may got to Dell
Bin 3's A step above radio shack
Bin 4's Radio shack
Bin 5's Rejects / scrap
So I often wonder if the same is still true today with all things.
We had 3 thread chasing sets, 1 Snap on @ $200+, 1 Mac tools @ $150.00 and a Craftsman set @ ~ $50.00
They appeared identical in every way including the box, instructions inside the lid, made in the USA etc. The only visible difference was the label on the outside of the box. Were they different quality? Only the unknown manufacturer would be able to answer that question.
