High-strength nuts are also called high-strength bolts, a type of standard parts, usually high-strength bolts can bear a larger load than ordinary bolts. The appearance and connection structure of high-strength nuts are basically the same as ordinary bolts. The basic working principle of high-strength nut connections is to deliberately add a very large tensile force to the bolts, so that the middle of the connected contact area is squeezed, so the screw rod is divided vertically There is a lot of friction in the direction, and this friction is used to transmit the joint shear stress. Generally, the bolted connection relies on the shaft to withstand pressure and bend to transmit shear stress. When the nut is tightened, the pre-tension force caused by the bolt is not large, and its impact is not considered; a simple summary is the pre-tension force of high-strength nuts. Be sure to tighten the nut and generally use the torque method and corner method. According to its bearing capacity, it can be divided into pressure-bearing type and friction type; these two types are actually different in the design calculation method. The friction type uses the rolling between the layers as the limit state of the bearing capacity, and the bearing capacity is normally used. The limit case is based on the rolling between the layers as a standard, and the friction nut cannot make full use of the potential of the nut. In specific applications, friction-type high-strength bolts should be used for key structures, especially those with internal stress in the opposite direction. At this time, the potential of the bolts can not be fully utilized as a safety reserve. In other areas, the pressure-resistant high-strength nut connection can be used to save construction costs. According to the classification of processing technology, it can be divided into large hexagon and torsional shear type; large hexagon belongs to the high strength of ordinary screws, and torsional shear type is an improved version of large hexagon, for better and faster construction. A nut, a bolt and a sealing ring constitute a twist-down high-strength nut. A nut, a bolt and 2 sealing rings form a large hexagonal strong bolt.