When a bolt is tightened into a mating threaded part, the two components interact by pulling each other together. This force is called clamp load and is what keeps the joint from coming apart. Provided that the force pulling it together is greater than the outside forces (service loads) that are trying to pull it apart, no problem will result with the attachment. Unfortunately, friction plays a large part in this system. Of the 100% of torque applied to fasteners to pull them together, 50% is lost in underhead bearing face friction and 40% is lost through friction between the mating threads. This leaves about 10% of the torque applied to actually pull the parts up to the required clamp load. The fastener's finish has a greater influence on tension than any other factor. Depending upon the coefficient of friction of the finish on the fastener, clamp load differences of more than 150% are possible on the same part. As Figure I (below) shows, a decrease of 10% in friction would decrease the underhead friction about five% and the thread friction about two%. While this does not seem like much, the decrease adds 70% more to the clamp load required.