A fixture is a work holding device, or a tool that holds a part in place while it's being CNC machined. When the part is simple, work holding is also simple; sometimes, the part can even be held in the machinist's hand. One of the most notable advantages is the ability to machine parts with particularly tight tolerances. CNC machining, which is extremely precise and replicable, can help ensure that there won’t be variability from one fixture to the next.