Screwdriver shaft and elevator: what they have in common

1. Step 1. Screwdriver shaft — is part of — Screwdriver. A steel rod.
2. Step 2. Screwdriver — uses — Screw thread. It drives screws.
3. Step 3. Screw thread — evolved from — Screw. A thread is an application of the screw.
4. Step 4. Screw — is a kind of — Simple machine. A screw is a simple machine.
5. Step 5. Simple machine — includes — Pulley. A pulley is a simple machine.
6. Step 6. Pulley — is part of — Elevator. The rope runs over a pulley.

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