Here is short explanation about producing a component contract in the GearCity game.
Component Contract: How It Works
A producing a component contract takes up a production line per model. When you win a contract, you go to assign it to a factory, and it will tell you how many it can build. You can assign more production lines to produce more units.
The game doesn’t tell you in advance the number of components you can produce in a factory line because it’s different based on the component and the factory’s ratings. And it isn’t an option before winning a contract because component production is not needed to produce cars in the game (yet, might come in the future).
That being said, normally it’s several hundred units built per production line. So unless it’s a massive contract, you shouldn’t need more than 1 line per component model.