Grill air vents and micrometer: what they have in common

1. Step 1. Grill air vents — is part of — Grill. They regulate the airflow.
2. Step 2. Grill — uses — Charcoal. Charcoal.
3. Step 3. Charcoal — is material for — Gunpowder. Gunpowder is a mix of saltpetre, sulphur and charcoal.
4. Step 4. Gunpowder — is used in — Revolver. Gunpowder propels the bullet.
5. Step 5. Revolver — uses — Interchangeable parts. Colt used machine production of interchangeable parts.
6. Step 6. Interchangeable parts — uses — Micrometer. Precise measurement ensures interchangeability.

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