What are inserts in machining?

Tool inserts can be made of industry grade diamond, and various other ceramics such as tungsten carbide - which is most common. Tungsten tips are made by pressing the powered material into the tool tip shape (usually a diamond/kite shape for turning tools, triangles for milling) and then heated so the particles bond to each other. These tips can be fixed to the tool body and then used to machine, on a lathe or mill. The advantage of tip tooling is if the tip breaks only the tip needs replacing not the whole tool, or having to grind the worn tool. However tungsten will not tolerate intermittent cuts as well as HSS, such as taking the corners off a square bar in a lathe.