Gas operation and telephone: what they have in common

1. Step 1. Gas operation — is used in — Machine gun. Gas-operated machine guns.
2. Step 2. Machine gun — has part — Spring. A return spring.
3. Step 3. Spring — is part of — Rotary dial. A return spring.
4. Step 4. Rotary dial — is part of — Telephone. A dial.

Open Evothings