Fixed-caliper brakes are being produced for two-wheelers, heavily exploited passenger cars, and for trucks (busses). The whole brake system, except for the pistons and brake pedals, is firmly attached to the wheel suspension. If the brake is operational, there is at least one pair of pistons pressing the brake pads against the brake disc. Due to the fact that there is at least one piston on each side, the brake fluid has to be transmitted from one side to the other. If this is done via the brake plier, the brake fluid might become very hot, so it is better to use an external connection.