The bolt represents the fastener which structurally includes the cylindrical rod having fine or coarse external thread of metric type, and head of the corresponding form (is defined by modern normative and technical requirements).
Bolts are applied to forming of strength and reliable detachable joint of various structural components made of tree, metal and plastic of the increased hardness. Such fastening elements are usually complemented with nuts and washers of spring or flat type.
Modern bolts are produced from stainless steel, solid plastic, various non-ferrous metals and their alloys, carbon steel both without additives, and with additives.
Producers release bolts of three classes of accuracy today:
1) raised (A);
2) normal (B);
3) rough (C).
The bolts having external metric thread are made or with small, or coarse pitch of thread. Considering ratio of length of rod of fastening element and length of its thread, distinguish bolts with:
1) imperfect thread;
2) full thread — it goes from the head basis up to rod face.
Considering the accuracy of production of bolts, external thread has to correspond completely to certain indicator of the field of its admission. At bolts of raised (A) and normal (B) of classes of accuracy this rate is 6g, and at products of rough class (C) — 8g.
The mechanical properties, for example, strength class which allows to define resistance of product to various dynamic and static loads arising at operation of the equipment or building constructions are characteristic of each bolt.
Classes of strength and accuracy are specified in the corresponding documentation where all modern standards for bolt fasteners are described.
Now bolts are widely applied in various detachable joints keeping the properties at operation in humid or arid climate with high, low or normal temperature rates.
The bolts made of carbon steel can be or with protecting cover, or without it. Thickness of layer of such covering and degree of his resistance to various aggressive external influences are defined by method of putting protective substance.
In the modern national economy use bolts both without covering (black), and with covering. It can be put with methods of galvanic, cold, hot and thermal diffusion galvanizing. The most durable and strong the zinc covering put with application of hot method is considered. It is capable to keep the operating ability for 50 years and even more. Electroplated zinc coating of bolts can have either protective, or at the same time decorative and protective properties. The second option except directly layer of zinc provides also additional layer of durability giving to fastening element characteristic shade.