Accuracy class bolts, nuts, high-strength fasteners
Fasteners are manufactured with coarse, normal and increased accuracy or accuracy classes C, B and A, respectively.
Each accuracy class has its own manufacturing tolerances.
For non-calculated mounting joints, fasteners of accuracy class C should be used, and for joints that perceive calculated forces, fasteners of accuracy class B and A.
Fasteners accuracy class C
Bolts, nuts of accuracy class C are placed in holes whose diameter is 2...3 mm larger than the diameter of the bolt rod. At the same time, the ease of placing bolts into holes with some mismatch of the walls of the holes of adjacent connected structural elements is achieved.
When an external force is applied to such a connection, significant displacements occur due to the difference in the diameters of the bolt and the hole, as well as the non-simultaneous entry into operation of all connection bolts.
For this reason, bolts of accuracy class C are placed structurally without calculations.
Fasteners accuracy class B
Bolts, nuts of accuracy class B are installed in holes whose diameter is 1- 1.5 mm larger than the diameter of the bolt rod. Therefore, such joints are less deformable compared to connections on bolts of accuracy class C and require higher accuracy in the formation of holes in the connected structural elements.
Fasteners accuracy class A
Bolts, nuts of accuracy class A are installed in holes that are drilled to the design diameter in the assembled elements and their diameter is greater than the diameter of the bolt rod by 0.25 - 0.30 mm, and the bolts themselves have only a minus tolerance for the diameter of the rod. Such bolts and nuts are made by turning and therefore have a high cost.
When a load is applied to such a connection, all the bolts come into operation almost simultaneously and therefore the connection is not very performative, however, it requires high precision of the holes in the connected parts.