...there is only so much you can say about a screw...
Agreed. That is a real dilemma, particularly if you have resellers who have more link juice than you do.
I've been adamant with several clients that they did need to add something extra... and they not only had to contractually specify to resellers that their web copy had to be different, but needed to create a different version for resellers. Fortunately, the products had more to be said about them than screws do.
My guess is that if your category pages are differentiated enough, your parts number pages are still likely to do well, but I've never been confronted with such a lean topic.