Horseshoe and conveyor belt: what they have in common

1. Step 1. Horseshoe — uses — Nail. It is nailed on.
2. Step 2. Nail — uses — Wedge. The point of a nail pushes the wood apart.
3. Step 3. Wedge — is used in — Sickle. The cutting edge is a wedge.
4. Step 4. Sickle — evolved into — Combine harvester. The machine replaced reaping by hand.
5. Step 5. Combine harvester — has part — Belt drive. Belt drives.
6. Step 6. Belt drive — is used in — Conveyor belt. The belt runs around the drive and tension drums.

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