Counter Boring operation basically enlarges a pre-drilled bore. Usually counter boring is used when machine power does not allow solid drilling of that size.It covers a large range of diameters up to 500mm. The number of cutting edges on the tool can vary depending upon the amount of stock removal. As the counter bore tool enters the component, the pads are supported by the finished bore diameter. The Coolant and chips flow is similar to BTA drilling operation or chip forward.