Flanged wheel and mechanical clock: what they have in common

1. Step 1. Flanged wheel — is part of — Wheelset. Two flanged wheels.
2. Step 2. Wheelset — is part of — Bogie. The bogie carries the wheelsets.
3. Step 3. Bogie — has part — Spring. Spring suspension.
4. Step 4. Spring — is part of — Vending machine. A spring holds the dispenser.
5. Step 5. Vending machine — evolved into — Parking meter. A payment machine.
6. Step 6. Parking meter — has part — Mechanical clock. A clock mechanism.

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