I tend to think from data table out, just the way I work I guess. If there are different types of specs for different types of items, you can either do separate dimension tables, or do one big table with enough fields to handle all the possibilities. I've gone both ways, and there are pros/cons with each. I've written an inventory system for the school district here, and it now uses one big table. Technical details, really.
First thing is to look at the sample data, and figure out how many types we're looking at, and how many fields are relevant. Might not be that complicated once we look at it. What are the types of items we'd be cataloging, and what are the relevant dimensions? Most fields (name, moss #, etc) are common to all, but what are the others?
bolt -- size, length, pitch, type? (Whitworth, BSF, etc)
washer -- diameter, size
pin -- size
We may find more commonality here than we think. I'm sure this could be expanded easily to encompass other cars as well, could be handy. Also, do we know if this already exists somewhere we can get to? Always hate to duplicate effort where possible.
This could be a fun little project.