The process known as boring is a machining process that enlarges an existing hole by means of a single-point cutting tool (or of a boring head containing several such tools), such as in boring a gun barrel or an engine cylinder. Boring is used to achieve greater accuracy of the diameter of a hole, and can be used to cut a tapered hole. Boring can be viewed as the internal-diameter counterpart to turning, which cuts external diameters. The boring machine has a single cutting tool or a boring head that contains several to many cutting tools.