The reason why a combination screw is called a non loosening screw is because it has an additional spring washer and flat washer, or only one spring washer or one flat washer, compared to ordinary screws. So, when choosing a screw, how to determine if this combination screw comes with a spring washer.
Flat pads are generally used for non vibrating power components, while elastic pads are used for vibrating power components; The function of the screw spring washer is to add a force to the screw cover, increase the friction of the thread, and avoid the occurrence of kickbacks; The function of the flat pad is to increase the contact area between the screw and the machine, reducing the damage of the spring pad to the machinery when removing the screw. To achieve performance, the flat pad of the combination screw needs to be installed below the spring pad at one end near the mechanical surface, with the spring pad located between the screw cover and the flat pad.
Combination screws are mainly used in railway and highway bridges, boiler steel structures, industrial plants, high-rise civil buildings, tower and mast structures, lifting machinery and their steel structures where friction type high-strength bolt combination screws are required.