Indexable cutting tools are machining tools fitted with removable cutting inserts. This is a typical tool that has a tool body or holder, a seat for the insert, the insert itself, and a screw or clamp to keep it securely in place.
The insert sits in a carefully made pocket so that it stays in the correct position during cutting. When one of the working edges wears out, the machinist can loosen the clamp or screw, and index the insert to another usable edge.
Some inserts can be flipped as well. Once all available edges have been used, the insert itself is replaced while the tool body can continue to be used.