Hole through a cylinder and aerosol can: what they have in common

1. Step 1. Hole through a cylinder — is part of — Cylinder seal. A hole for the cord.
2. Step 2. Cylinder seal — works like — Gutenberg printing press. An analogy: both a seal and a press reproduce a pre-carved pattern.
3. Step 3. Gutenberg printing press — evolved into — Rotary printing press. Cylinders instead of a flat press.
4. Step 4. Rotary printing press — has part — Watt steam engine. The first rotary presses were steam-driven.
5. Step 5. Watt steam engine — has part — Valve. A slide valve distributes the steam.
6. Step 6. Valve — is part of — Aerosol can. A valve.

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