How fine thread can be called fine thread? We may wish to define it this way. The so-called coarse thread can be defined as a standard thread; and the fine thread is relative to the coarse thread. Under the same nominal diameter, the number of teeth per inch is different, that is, the pitch is different The pitch of the teeth is large, while the pitch of fine teeth is small. In other words, for the 1 / 2-13 and 1 / 2-20 specifications, the former is coarse teeth and the latter is fine teeth. Therefore expressed as 1 / 2-13UNC and 1 / 2-20UNF. Since there are two different thread sizes for the same nominal diameter, how to choose coarse and fine thread?
The so-called coarse teeth actually refer to the standard thread.
Without special instructions, the fasteners such as stainless steel screws that we generally buy are coarse teeth. The characteristics of coarse thread are high strength, good interchangeability, and there are standards for comparison.
Generally speaking, coarse teeth should be used as the best choice; Compared with the fine thread, due to the large pitch and the large angle of the thread, the self-locking property is poor. In the vibration environment, it is necessary to install a lock washer and a self-locking device. , Easy to interchange;
The pitch of coarse thread need not be marked, such as M8, M12-6H, M16-7H, etc., mainly used for connecting thread.
Fine teeth and coarse teeth are exactly the opposite. They are stipulated to supplement the special use requirements that coarse teeth threads cannot meet. Fine teeth threads also have a pitch series. The pitch of fine teeth is smaller, so its characteristics are more conducive to self-locking and anti-loosening And the number of teeth is more, which can reduce the effect of leakage and achieve the effect of sealing. In some precision occasions, fine-tooth stainless steel screws are more convenient for precise control and adjustment. The disadvantage is that the tensile value, the strength is lower than the coarse teeth, and the thread is easy to damage. It is not recommended to disassemble and assemble multiple times. The matching nut and other fasteners may be equally accurate, with a slight error in size, which can easily damage the screw nut. Fine thread is mainly used in metric pipe fittings of hydraulic system, mechanical transmission parts, thin-walled parts with insufficient strength, internal parts restricted by space and shafts with high self-locking requirements. When marking fine threads, the pitch must be marked to show the difference from coarse threads.
How to choose thread thickness Use coarse and fine threaded screws for tightening.
Fine-toothed screws are usually used to lock thin-walled parts and parts with high vibration requirements. The thin wire has good self-locking performance, so it has strong anti-vibration and anti-loose performance, but because the depth of the wire is shallow, the ability to withstand a large pulling force is worse than that of the thick wire. When no anti-loosening measures are taken, the anti-loosening effect of the thin wire is better than the anti-loosening effect of the thick wire, and it is usually used for thin-walled parts and parts with high vibration requirements. When used for adjustment, fine threads have more advantages. Disadvantages of thin lines: not suitable for materials with too thick tissue and poor strength. When the tightening force is too large, it is easy to make the wire slip.