You might find a data model here that will work for you (no sense recreating the wheel, I always say). Use your browser search function to find the ones that deal with parts. If none of them help, post back for more help. At the very least, they should provide some food for thought, and thus meaningful questions. One thing you have to realize is that spreadsheet type design does not a good table make. So if you have Excel brain, you will have to be re-programmed!
IMHO, forms come after proper table and query design as I seldom base forms on tables alone. So if data can't be added through a normal query, it is often a sign of table design problems, meaning the form already created is possibly useless. Certainly, there are things you could do wrong at the start, thereby making progress more difficult than it needs to be - things like multi value fields, lookup fields (in tables), poor naming convention, etc.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.