Many important considerations in bolted joint development are often overlooked. While estimating the bolt tension achieved for a given tightening strategy is certainly a common focus, the effect of load on joint components is less fully discussed and understood.
One reason threaded fasteners are so widely used is that they can generate a tremendous amount of clamp load in a small area. Clamp load is central because it is the mechanism by which joint components are held together without moving relative to one another—arguably the primary requirement of a structural joint. However, placing a large load on a small area creates a high level of stress, which, in turn, can lead to problems. For example, a ½ - 20 Grade 8 bolt can supply nearly 20,000 pounds of clamp load. A standard hex head bearing on a standard 9/16-inch clearance hole means all that load would act on an area only half the size of a dime. The resulting stress exceeds the yield strength of most materials. An analogy is the effect spike heels can have on wood floors.