Disc brakes consist of a metal disc attached to the wheel hub that rotates with the wheel. Callipers are attached to the frame or fork along with pads that squeeze together on the disc. The primary benefit of disc brakes is that they perform equally well in all conditions including water, mud and snow. This is due to their position closer to the hub and away from the ground. Bicycle disc brakes consist of a metal disc attached to the wheel hub that rotates with the wheel. Brake calipers are attached to the frame or fork along with pads that squeeze together on the disc. The way it is attached to the bike will be either by IS (International Standard) which has two holes facing the disc or Post Mount, which has threads going into the fork. Such brakes have been successfully used on motorcycles for decades, and are the principal choice there. They are finally becoming more popular on bicycles. Recent material advances in weight, costs and reliability have led several firms to develop and implement disc brake systems, and those are becoming a standard feature on many bicycles. They are used mainly on mountain bikes ridden off-road, but sometimes on hybrid bicycles and touring bicycles.