Attributes, quantities and handling an assembly

[Wade C]

I have products that are a base product that doesnt change, but has three options for each base product. And the base product is the quantity limit

I read where you have to change quantities in the attributes for that base item... my problem is that in this case, the limiting factor is the quantity of the base item.

For example:
I have on hand 10 drill chucks
A person can buy the drill chuck with one of three (attributes) arbors on it a MT1, MT2, or a MT3
I keep on hand 20 or 30 of each arbor as they are used in other products, and I combine the appropriate arbor with the drill chuck when I ship out. So in reality, I theoretically have 10 of any of the three versions in stock, but if one of the attributes is used, then I have only 9 drill chucks left.

I can think of one logical change - but the flow on the site is not intuitive.
Change the base item to the three different items, the arbors, ie. item1: 1mt, item2: 2mt, item3: 3mt
and then make the drill chuck the attribute. THat I think would work, but the screen flow would not make much sense to a newbie in my "industry"

Is there another approach that I am not thinking of to fix this?

Thanks