Steel blade and watt steam engine: what they have in common

1. Step 1. Steel blade — is part of — Knife. A blade with a cutting edge.
2. Step 2. Knife — is part of — Meat grinder. A cross-shaped blade.
3. Step 3. Meat grinder — has part — Crank. A handle.
4. Step 4. 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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