Why use a threaded insert?

Threaded inserts are typically used when the object in which a threaded fastener is being fitted is made of a soft material. For harder materials, a screw or bolt can be often driven into the object without the need for a threaded insert. However when using softer materials driving a bolt or screw directly into the object can cause damage. The easiest solution is to use a threaded insert. The threaded insert is placed inside the object, then the threaded fastener is driven into the insert.

Another reason is when an existing threaded hole is stripped. If the ridges of a threaded hole have worn away to the point where they no longer support or hold a threaded fastener, a threaded insert can be used.