I-beam and autoclave: what they have in common

1. Step 1. I-beam — is made of — Wrought iron. The first I-beams were made of wrought iron.
2. Step 2. Wrought iron — is material for — Boiler. Later — made of sheet wrought iron.
3. Step 3. Boiler — is part of — Autoclave. A steam generator.

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