Park's Offset Brake Wrench utilizes a unique design that allows it to reach into tight areas that other wrenches cannot. The OBW-3 features a 14mm wrench on one end and the other end fits into a brake's tension springs to rotate the brake around its bolt for proper alignment. The OBW-4 features 10-, 11-, 12-, and 13-mm opening to fit most models of sidepull brakes.