Quality control. Each component is made to specifications, and if it doesn't meet specification, it gets tossed/recycled.

For example, car needs a 50.00mm +/- 0.01mm rod in length, 10.00 +/- 0.01 mm in diameter. Worker makes 10 rods. Quality control checks them, finds that one rod is 50.05 mm long when max permissible is 50.01. Tosses it.