Hi. The general principles of using multiple combo boxes which are cascade-filtered are given in our howto article on
cascading combo boxes.
However, you may struggle to produce source queries which can be suitably filtered, given the apparently manual way you currently seem to build your part number string.
If I was doing this I would think long and hard about how the part number is intended to match the product. To get a better view of how this is done I would write down a decision table - just on paper - to clarify what the patterns involved are. If the rules for producing the part number can be codified then they can be automated using Access. If the rules are difficult to write down manually then it will be difficult if not impossible to get Access to do the job for you, as cascaded combos have to have a defined source that is filtered from one cascaded combo to the next - no good if you can't define how the filtering is to work.
After defining the rules for the part number I would tend towards using a custom function written in VBA which takes the necessary data from whatever defines the product and generates a part number for the product automatically - perhaps in conjunction with a table of unique numbers if needed. In any event, if I was you I would define the rules and be absolutely clear about what it is you want to be implemented before going any further.
-Stewart
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