The task of a bolt is to connect two or more components. This happens due to the axial bolt pretensioning force. But what is the axial pretensioning force? What is a thread? Basically, a thread is a sloping level which is wound up. If you screw a nut on the bolt thread, it follows this sloping level – the flank lead. When the nut reaches the flange you generate bolt elongation and flange compression by further screwing. This bolt elongation is the aforesaid pretensioning force and is a result of the stretched bolt material. Taking a close look at the pretensioning force generation, usually it has impact on the nut due to a torque. This equals a torsional stress on the bolt, which works against the bolt in its actual function. That is the reason why Bolt Tensioners, Hydraulic Nuts and Multiple Stud Nuts are used, which do nothing else than pretensioning the bolt purely axial and torsion-free.

In general although, any pretensioning force generation does not only elongate the bolt shaft, but also the thread. A distortion of the heavily loaded thread occurs, which does not comply with the original geometry of the nut anymore.

The patented idea of SCHAAF GmbH & Co. KG is to copy the profile of the highly pretensioned bolt thread in the nut area and to transfer it to the nut with the exact change of geometry.

What is the result? The whole flank surface of the bolt has an equally exact contact with the nut with TTG thread. Therefore, there is no stress concentration as before in the first thread turns where nut and bolt touch. Instead, the pretensioning force distributes equally over the complete geometry. Highly stressed threads, which are mostly charged with additional dynamic load, receive a higher longevity, higher safety at same component size and with insignificant higher costs.