Crutch handgrip and bellows: what they have in common

1. Step 1. Crutch handgrip — is part of — Crutches. A grip for the hand.
2. Step 2. Crutches — evolved into — Wheelchair. Mobility aids.
3. Step 3. Wheelchair — has part — Ball bearing. Bearings.
4. Step 4. Ball bearing — is part of — Conveyor belt. The rollers turn on bearings.
5. Step 5. Conveyor belt — is made of — Leather. The first belts were leather.
6. Step 6. Leather — is material for — Bellows. Bellows are a leather bag.

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