A jar and its lid have threads that fit together.
Hold on Tight
Screws come in many different shapes and sizes. How do you take off the lid from a jar? You unscrew it! A lid is a screw.
Screws keep more than lids tight. The stem of a light bulb is a screw. The threads of the stem turn between the threads in the socket. The threads keep the bulb in place.
That’s a good thing, too! Light bulbs in the ceiling hang upside down. If they slip out, they might fall onto your head!
The threads on a light bulb stem screw into the socket of a light.
A drill bit is a screw! Can you see the thread?