Grain and micrometer: what they have in common

1. Step 1. Grain — is used in — Reaper. The reaper cuts the grain crops.
2. Step 2. Reaper — has part — Crank. A crank moves the knife.
3. Step 3. Crank — is part of — Cotton gin. The drum was turned by a handle.
4. Step 4. Cotton gin — uses — Interchangeable parts. Whitney was one of the promoters of interchangeable parts.
5. Step 5. Interchangeable parts — uses — Micrometer. Precise measurement ensures interchangeability.

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