Hello, I am not certain about your Relationship diagram as I can't see the reason for 3 partslists, or for the other 3 tables between the parts lists and the assembly.
Is it possible to upload the database for me to look at?
If the data is sensitive you could take a copy and delete the data and then create a couple of dummy records for me to play with.
What version of Access are you using, as I need it to be in Access 2007 format.