A bolted joint is a separable connection which is intended to join two or more parts in such a way that they behave as one part under all operating conditions. The operational safety of the connection can be guaranteed only by precisely matching the calculation and dimensioning of the bolted joint to the methods used for assembly and bolt tightening. Preservation of an adequate residual clamp load is a decisive factor for operational safety. There is a risk that a bolt will loosen or even break under load if the forces acting during operation reach a level where they cancel out the clamp load.

In the simplest case, a bolt joint can be represented as a tension / compression spring construction. The bolt corresponds to the tension spring and the parts to be fastened (e.g. two metal parts) are the compression spring.

When the bolt is tightened, it is correspondingly elongated by the action of the assembly preload of the tension spring. The clamp load acts on the parts which are to be bolted together (compression spring) and presses these parts together.

Normally, tightening causes a greater amount of bolt elongation than compression between the parts. The preload applied in assembly elongates the bolt by the an amount, while the parts which are bolted together are pressed together (compressed) as a result of applied tightening forces.