Book 3, Question 131
Why Do Nails Have Points and Screws Have Threads?
Nails have points so they can be tapped in like a wedge, and screws have threads so they twist in like a ramp.
A nail is a wedge that you tap. A screw is a ramp that you twist. Both hold wood together, but they grab in different ways!
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From the book
Page from A Million Whys Book 3
More fun facts
- A nail with a long, sharp point usually holds tighter than a common nail, especially in softer woods.
- But a sharp point can split some kinds of wood, which makes the nail hold less.
- A blunt point splits wood less, but it crushes the wood fibers, so the nail holds less tightly.
- Smooth nails can lose a large part of their grip when wood dries out or gets wet and dry again.
- Nails with ring shaped threads can hold up to twice as strongly as common nails.
- A screw has a head, a shank, a thread and a core.
- The deeper a screw's threads go into the wood, the harder it is to pull out.
- Some screws have a drill shaped tip, so they can cut their own path through wood and even steel.
Sources: U.S. Forest Service
Questions kids ask
Why do some nails have rings on them?
The rings grip the wood, and ring nails can hold up to twice as strongly as common smooth nails.