Screws

A screw is a simple machine that looks like a nail with ridges. These ridges are called threads. A screw is really an inclined plane wrapped around a rod. Screws are used to hold things tightly together or to lift things up.

How Screws Hold

When you turn a screw, the threads pull it into the wood or metal. Each turn pulls the screw in a little more. The threads grip the material and hold it tight. Screws are very strong and hard to pull out. That makes them great for holding things together.

Different Uses

Screws are used in many ways. Builders use them to join pieces of wood. Jar lids use screws to seal tightly. Light bulbs screw into sockets. Big screws called augers drill holes into the ground. Some old machines even used screws to lift water up from rivers.

Fun Facts

• Archimedes invented a giant screw to pump water out of ships.
• Some screws are so tiny that you need a microscope to see them.
• A spiral staircase works a lot like a screw.

Did You Know?

If you could unwind the threads of a screw, they would stretch out into a long inclined plane.