Screw lamp base and saw: what they have in common

1. Step 1. Screw lamp base — is part of — Incandescent light bulb. A screw contact (the Edison base).
2. Step 2. Incandescent light bulb — evolved from — Gas lamp. Electricity displaced gas lighting.
3. Step 3. Gas lamp — has part — Valve. A gas supply valve.
4. Step 4. Valve — is part of — Internal combustion engine. Valves let in the mixture and let out the gases.
5. Step 5. Internal combustion engine — is part of — Chainsaw. A two-stroke engine.
6. Step 6. Chainsaw — evolved from — Saw. A mechanized saw.

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