A die grinder is a handheld power tool used to grind, sand, hone, polish, or machine material, typically metal but also plastic or wood. They are usually pneumatically driven, although versions with electric and flexible shaft drive also exist. Their name comes from one of their earliest and archetypal applications, tool and die work, where they are used to create the precise contours of dies or molds. Especially before the advent of widespread CNC usage, they were heavily relied upon for contouring via manual skill comparable to a sculptor's. CNC now provides much of the contouring for die and mold interior surfaces, but die grinders are still very useful for hundreds of cutting needs, from sculpture-like contouring in the absence of CNC, to cut-off of bar stock, to any of the cutting and grinding needs of fabrication, such as in the work of welders, boilermakers, millwrights, ironworkers (steel erectors), sheet metal workers (such as auto body workers and HVAC technicians), to woodworking (especially cabinet making), hacking, and other hobby or business pursuits. Die grinders are often used for engraving, cylinder head porting, and general shaping of a part.