Jack and rolling mill: what they have in common

1. Step 1. Jack — has part — Check valve. Check valves.
2. Step 2. Check valve — is part of — Bellows. An air intake valve.
3. Step 3. Bellows — is part of — Blast furnace. Air was blown in by bellows, later by blowers.
4. Step 4. Blast furnace — is part of — Steel works. Blast furnaces.
5. Step 5. Steel works — has part — Rolling mill. Rolling mills.

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