Scythe hand grip and internal combustion engine: what they have in common

1. Step 1. Scythe hand grip — is part of — Scythe. A crosswise handle for gripping.
2. Step 2. Scythe — evolved from — Sickle. Mowing while standing, with a long snath.
3. Step 3. Sickle — evolved into — Combine harvester. The machine replaced reaping by hand.
4. Step 4. Combine harvester — has part — Roller chain. Chain drives power the working parts.
5. Step 5. Roller chain — is part of — Chainsaw. The cutting chain is a roller chain with teeth.
6. Step 6. Chainsaw — has part — Internal combustion engine. A two-stroke engine.

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