Helical screw blade and knife: what they have in common

1. Step 1. Helical screw blade — is part of — Archimedes’ screw. A spiral that lifts water as it turns.
2. Step 2. Archimedes’ screw — evolved into — Auger. The Archimedes’ screw as a conveyor.
3. Step 3. Auger — is part of — Meat grinder. An auger.
4. Step 4. Meat grinder — has part — Knife. A cross-shaped blade.

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