Screwdriver shaft and watt steam engine: what they have in common

1. Step 1. Screwdriver shaft — is part of — Screwdriver. A steel rod.
2. Step 2. Screwdriver — uses — Torque. The handle creates torque.
3. Step 3. Torque — is used in — Planetary gear. It transmits rotation through planet gears.
4. Step 4. Planetary gear — is part of — Watt steam engine. Watt’s “sun and planet” gear got around the patent on the crank.

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