Jack and David
One kind of simple machine is a screw. A screw is a simple machine that looks like a nail with ridges on it. The chairs need screws to stand up. A screw is made out of metal. A example of a screw is a water bottle cap. A screw is very helpful.
Screws make life easier
A screw is a simple machine that looks like a nail with ridges. The lids of some jars are screws. Inside the lid the screw helps hold things in place. Screws hold things in place. Screws hold swing sets in place.