Suppose you went out tomorrow and bought a brand new car, suppose for some crazy reason you bought a Ford. On the front and back it would say “Ford” and even the middle of the wheels would probably proclaim their Fordiness. If you looked under the bonnet you would probably see a big “Ford” cast into the rocker cover, and if you took the air filter out you might see some long ass product code and the word Ford. With the possible exception of the tyres every part of the car would have been specified and designed by Ford for that car and as a result it will all fit nicely together first go.