A fastener is a device used to hold two or more objects together securely. Common types of fasteners include screws, bolts, nuts, and rivets. They are essential in construction, manufacturing, and everyday items, ensuring that parts stay connected and function properly. For example, a screw can attach a door handle to a door, allowing it to operate smoothly. Fasteners come in various shapes and sizes, designed for specific tasks. Some are made from metal for strength, while others may be plastic for lighter applications. Understanding the right type of fastener is crucial for projects, whether you're assembling furniture or building a treehouse.