Precision micrometer screw and watt steam engine: what they have in common

1. Step 1. Precision micrometer screw — is part of — Micrometer. A 0.5 mm pitch.
2. Step 2. Micrometer — is used in — Interchangeable parts. Precise measurement ensures interchangeability.
3. Step 3. Interchangeable parts — is used in — Cotton gin. Whitney was one of the promoters of interchangeable parts.
4. Step 4. Cotton gin — has part — Crank. The drum was turned by a handle.
5. Step 5. Crank — is part of — Watt steam engine. The stroke of the piston becomes rotation of a shaft (Watt first used a planetary gear).

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