Interchangeable parts and needle: what they have in common

1. Step 1. Interchangeable parts — is used in — Cotton gin. Whitney was one of the promoters of interchangeable parts.
2. Step 2. Cotton gin — has part — Crank. The drum was turned by a handle.
3. Step 3. Crank — is part of — Sewing machine. A crank turns rotation into the stroke of the needle.
4. Step 4. Sewing machine — has part — Needle. A needle with the eye near its point.

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