Periscope and lathe: what they have in common

1. Step 1. Periscope — is part of — Tank. Observation devices.
2. Step 2. Tank — has part — Tank gun. A gun in a rotating turret.
3. Step 3. Tank gun — has part — Rifling. Rifled tank guns (today often smoothbore).
4. Step 4. Rifling — uses — Screw thread. Helical grooves.
5. Step 5. Screw thread — is used in — Screw-cutting lathe. The lathe cuts precise standard threads.
6. Step 6. Screw-cutting lathe — evolved from — Lathe. Maudslay added a lead screw and a slide rest.

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