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Why Does the Fastener Have Back Buckle?

Nov. 27, 2020

As an Anchor Bolt Manufacturer, share with you.

In daily life, many friends find that when they loosen the screws, they will find that the more they are tightened, and after trying left and right, they found that some screws are unscrewed counterclockwise. Why does this happen? The reason is that the screws have positive and negative threads. The division of silk can also be called positive buckle and reverse buckle.

China Anchor Bolt

China Anchor Bolt

Comparison of left and right threads

The positive buckle is common. Tighten clockwise and loosen it counterclockwise. However, the reverse buckle is rarely used. The tightening method is the opposite of the positive buckle. Reverse screws are generally made according to needs and requirements, usually to prevent turning back. According to the direction of rotation, it is less likely to cause torque attenuation than a right-handed screw and is more reliable.

Rectangular screw

The scientific name of the back buckle is "left-handed screw". As the name implies, it is the opposite thread to the normal fastener screw, also called "reverse wire". The normal fastener screw is tightened clockwise, and the back buckle is to be tightened. It is screwed counterclockwise, and when it is loosened, it is screwed clockwise. Then why are there "reversed" fasteners? What mechanical equipment are "reversed" fasteners generally used for? Today I will talk about it. "Back button" fasteners.

Reverse fasteners are usually used in rotating mechanical equipment, such as fan blades, impellers in motors, vertical mills, bicycle left pedals, air-conditioning fan impellers, etc. There are also “left-hand screws” that are rarely used for safety reasons, such as pressure relief valves for flammable gas tanks.

Gas tank pressure reducing valve

The thread is screwed in when rotating clockwise by default. If it is screwed in when rotating counterclockwise, it must be explained. In addition to marking LH (or L) in the thread specification, the description method can be described in the name, such as left-hand thread and reverse screw. The method of identifying the left-handed and right-handed threads is to stand the screw upright and observe the thread direction.

A simpler method is to hold the screw with your right hand. If the spiral angle of the thread is toward the thumb, it is a positive buckle, and vice versa. However, the anti-wire screw usually has an engraved logo, so you can pay attention to it.

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