Reusable rocket and micrometer: what they have in common

1. Step 1. Reusable rocket — has part — Liquid-propellant rocket engine. Liquid-propellant engines.
2. Step 2. Liquid-propellant rocket engine — evolved from — Rocket. Goddard switched to liquid fuel.
3. Step 3. Rocket — uses — Gunpowder. The first rockets were powered by gunpowder.
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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