That's really interesting, and something I didn't realize. I know in the case of Ryobi and Hart power tools, both are made by TTI. Are you saying in that instance they subcontract out the work, or are you referring to a different class of tools?
TTI probably makes Ryobi and Hart on the same assembly line. 80% of the parts will be the same. They will put a different case on as they come down the line. They might also have other differences inside, like a different set of gears (which match the case so you can't always mix and match). It costs more to support different products on the assembly line, so there are trade offs. It is quite likely that they started with the design for one to make the other.
Note that I don't have any insight into TTI, just that the above is the normal way companies operate.
